Well, they said Turn 10 ported FH6 easily, and that it ran at 4k, 60fps and with a good chunk of power yet left to be used. So I guess it's safe to say most games current gen could run 1080p 60 fps without much effort.
From the article on the topic of third party titles:
Microsoft says that while the porting work will be more involved, these too should hit native 4K.
More involved = more effort.