It's probably been suggested before, but I just noticed this when playing my version of the Bardovkas. In 1279, the Ilkhanate has a Nestorian ruler by the name of Abaga Borjigin. I did a quick search on the internets, and couldn't find much (anything) on him, but I don't think Paradox would've just put in a random Nestorian Khan in a non-bookmarked location. Either way, starting in 1279 you can play as a Nestorian Ilkhanate who has a surprising number of Nestorian vassals as well. Though familial problems do persist, and your son stays true to the Old Ways. With a large number of pissed off vassals, an aging ruler, and a son who doesn't follow his religion, it'd make for an interesting playthrough.