With the unthinkable (finally) happening, we now have full cross-play between all consoles. Granted, it's currently only Fortnite and Rocket League, but it won't just stop there (presumably). I think, if it is technically possible (big if), The Elder Scrolls Online would be a nice choice for another cross-play game. Bethesda supports that game like crazy and are constantly adding to the game. If it did come, I would surely hope it would also have cross-save/cross-progression and cross-buy (for DLC), but I don't think the platform holders would ever go for the latter. I got it a while back on PS4 (have spent many, many hours on it) and then on PC (via Humble Bundle). I've barely touched the PC version, but if my PS4 character and progression could be brought over, I'd be all over that.