It's gonna be quite a challenge indeed..

I don't think setting the (first) game far in the past history would work that great. It's an interesting choice for later releases if it becomes a franchise, but a game that doesn't have the familiar cultures, locations, factions etc. would be a huge let down to the part of the buyers who aren't big gamers and who rather buy the game more for the "WOT-universe immersion experience". The TW era is too different from the New Era. Cities wouldn't be those we know nor even in the locations of the current big cities, politics are wholly different, even WT culture is very different. No usual suspects, like the Whitecloaks. It would be a good setting for a strategy game, but it's terribly limited in potential for RPG, at least if the developper want an open world offering a lot of freedom instead of tying the player to a quest (and it would not be WOT-like enough for most fans, I suspect. Pretty much only the players who want to play a channeller and kick-ass would find some fun in that.)

Setting the game post-TG? Well, you pointed out well the problems. A post TG game would also be difficult to make at this point, anyway. I doubt Harriet would allow it for now and until the final decision is made about the "outriggers" and all. It would have to be a wholly fictitious post-TG RPG, that in a few years might contradict completely the real ending.

A game set in the timeline of the series condemn the developpers to either push too much of the series' events aside and limit the gameplay to sideshows while the epic stuff goes on in the background and away from the player's game, or else to integrate too much of it and lose way too much of the freedom to develop a good game, following the "main beats" of the series instead. And well... whatever you do you won't be Rand or Egwene or Mat, and it's on them the Forsaken are focussed etc. It wouldn't be easy to open the world to the player and avoid bumping too often on events the series, also.

Personally, I think the style of game that would probably fit the series best and please the largest number of people (experienced gamers who are fans and WOT fans who aren't much gamers but would become addicted to that game because it's WOT) would be a game very much like Morrowing/Oblivion, as intricate and involving, and with as much freedom to approach the game in your own style and at your own pace, and get out of it the sort of experience you want. Re-playability is also excellent with a game like that.

Players who want to build up a super channeller and spend most of their time facing rogue channellers, emptying the Blight or hunting down caches of OP objects could do so in a game like this.

People who want to be let free to do what they want in the world can, those who like to do a bit of that but also be more "directed" can create themselves a Blue sister and spend hours and hours on a long series of side-quests given by the Ajah Head, the Amyrlin, nobles and people who ask for help in towns and villages. Find yourself a warder, avoid BA plots and interference by other sisters, DF, Whitecloak agents and so on. Or work your way up to become the best blade in the land, train under great blademasters, fight in quests and gain so fame, stay your own man to your death or attract some kick-ass Green that will become your partner in quests as your Aes Sedai.

Or you can be a Domani trader making your way up the Merchant house you belong to, travelling the world in a variety of trade-like qests.

Or you could be a Brown and spend your time searching the libraries, bookstores and caches of books all over the land to find all sort of secrets. Find obscure old statues and caves, open the ways, go observe Shadar Logoth, talk to all sort of people in cities for information, gather the biggest collection of ter'angreal and try to make them work. Borrow Verin's ring and explore TAR. Etc.

You can be a Yellow and hunt down the wounded and sick to perfect your Healing skills. Or you can be a Kinswoman, travelling all over the place as a trader, or settling down in a small village as Wisdom, training your channelling in secret, avoiding being spotted. Visit Ebou Dar to change your identity if you've attracted unwanted attention... If you're a Wisdom, buy your ingredients at shops, or roam the woods and bizarre places for them. Etc.

You can start as a full sister, or be a young girl with the spark, who make her way to the WT, goes through novice training, pass the Accepted test and eventually the one for the shawl. Avoid being recruited by the BA... or try to make yourself a candidate for them if your ambitious.

You can be a soldier from most lands, performing quests for your ruler. You can be a Hunter for the Horn, exploring the land to your heart's content.. You can make yourself the new Jain Farstrider.... or a gleeman.

You can be a spy-assassin for any number of factions... Shadow, Whitecloaks, merchants, some of the rulers etc.

Heck, you can even just set up an Inn somewhere and spend your time hearing the tales sof travellers.

An Oblivion-like game can have a main quest (for e.g. involving Ishamael and others), and many hundreds of side-quests, all the cities and nations, the whole WT to explore or live in, tons of villages and remote places. It can have a big fight engine, a wide range of traditional combat possibilities for "soldiers" and spy-assassins/thiefcatchers types, and the full OP spectrum for channellers.

Done right (it needs to be as good as Elder Scrolls if not better, which is putting the bar very high - especially that the best choice of partner for something like this would have been Bethesda...), a game like that would be awesome.

There are a few options to get rid of the "main story line" but retain as much as possible of the "WOT experience". One of them would be to set the game a bit in the past, but not to far away not to lose the familiar setting.

A good choice (IMO) would be to set it just before the fall of Malkier, while the Shadow is plotting to make that event happen: preventing the fall (or helping it if you are BA etc.) could be the "main quest", to approach very differently depending on your character's class (and of course in a game like this you can ignore the main quest altogether). The fall of Malkier is familiar, but it lends itself quite well to a web of side plots and conspiracies from the Shadow. It also offers a range of (non-playable) familiar players the fans would be happy to meet in cameos. A lot of nations would be ruled by Houses we know, many sisters like Romanda, Verin, Cadsuane etc. would be at the Tower, but the developpers would have near complete freedom with them, as we know little of what they were up to in those years (well... Verin was already hunting the BA, which can be used).

The big downside is that the developpers would be constrained to rogue male channellers only, and to Ishamael and invented DF/BA bosses as big foes. Saidin-users would be non-playable, foes for the Red Ajah players. That would feel very WOT-like, but might irritate some male players to have to play a sister or Kinswoman if they want to channel (that one of the downsides of WOT as a RPG settting: the majority of gamers are male, the best characters to play in WOT are women).

Another option might be to set the game around the time of Rand's birth. A great deal more familiar characters would thus show up as cameos (Morgase would be Queen, and Moiraine away hunting down Rand but Sierin would be Amyrlin, and Siuan could be used as a WT NPC who gives quests, but the main quest might have to be centered on the BA and the vileness, forcibly. Still no saidin users.

Another alternative would be to set the game in an If World, perhaps around the time of TGH (there's plenty of unrest already, the Seanchan are in the West but still only on Almoth, not in the whole south etc. Lanfear and Ishamael are already around, but not the whole cast of Forsaken who can be kept for later games, like the playable male channellers. One event or another from the series hasn't happened and this triggered the creation of this IF World the game is set in, and the whole Pattern might be woven differently in that world. The three boys are lost between "if worlds" and not involved in the game, the girls are captives in Falme. The WT is already full of plots and schemes, the BA trying to take over. Ishamael has called a hundred DF to a meeting, and there's plenty of rooms there to create tons of plots involving the Shadow. The setting of the game would be very faithful to WOT and the general backdrop of TG coming would be there (no need to make the first game about TG...) but the "if world" device would take care nicely of getting rid of all the constraints of the main players and main storylines, letting the player have fun with the familiar world. A good compromise, if the game they have in mind is a WOT-version of Elder Scrolls.