What do you think, all else aside, of the show's apparent (I'm not sure if they ever say it explicitly) decision to make all five of the Emond's Fielders ta'veren instead of just the three in the books?

It's not something I hugely care about one way or the other, but I think it makes more sense for all five to be ta'veren-level important to the Pattern. Egwene and Nynaeve's discoveries in the Power seem at least as important as Perrin's contributions, though I suppose Nynaeve's advances in Healing are much more important in the long term and much less important in regard to the Last Battle.