I'd vote for an I4, simple easier to work on, last for ever. The Wankel is a neat idea but short life. Why is a V6 used? Miserable contraptions to service.
If they shoehorned an I4 into the engine bay, it wouldn't be simple or easy to work on. The hood would have to get raised, plus they'd have to turn it sideways and ditch everything that's Subaru about the Subaru containing it.
I do agree about the short life of existing Wankels, and they're not really something that entertains me too much, I just know that they're getting kicked around again. No idea of somebody is going to overcome their quirks, or if it's just getting kicked around. But there IS a very large amount of horsepower available that way in a VERY small package. Probably that's why they didn't die as soon as the first ones out almost immediately proved their shortcomings.
Subaru with a V6? H6 (flat six) I think. They couldda snuck one by me, I don't think so.... It's have to be the Ascent, but I don't think they could even squeeze a V motor into that one without designing a completely different car.