They came for WOT discussion and stayed for Community. Splitting up the boards just segregates people who won't then "spill over" into the community.
What's going to draw people in? The "segregation" argument doesn't make much sense, unless one wants to argue that people self-segregated or, conversely, were ostracized at wotmania for their posting preferences. I just know there were several SF/F bloggers who got their start over at OF who didn't really participate in "community" stuff because it was a bit insular then and I suspect it'd be even more insular now.
But that's just my perspective on matters. I'm not really active much anywhere these days (the past weekend being a mini-exception), so either way doesn't mean much to me other than a vague desire that even the remnant of the old OF might live on, I suppose.
The worst think that Mike ever did was to split the boards. OF should never have been split off of community just as WOT should never have been split off either. It was better to keep it mixed and to see the cross pollination going on.
Yes, the rise of FB also meant that people didn't have to interact at wotmania. But for a time before the boards were split there and here, and before people could ignore each other here, you saw everything. You didn't ignore anyone. And maybe your opinion about someone changed over time.
As to what will draw people in? Probably more discussion of Sanderson. He seems to be the spiritual heir to Jordan. Especially given his fantastic world building in the Cosmereverse that he has created.
I should probably suggest a book club discussion of The Way of Kings and Words of Radiance before Oathbringer comes out in November. Once the boards are combined.