I disagree. It will probably not look as good as late games that were tailor made specifically for last-gen. Cross-gen games usually don't.
I think it will look as good as multi-plats designed for last-gen.
A recent example would be Forza Horizon 2. According to folks it looks worse than the original on 360.
I think this is just a case of them having seen Forza 2 on XB1 where it looks amazing (literally AMAZING) and a case of the terrain being slightly different in terms of the actual level design. When you compare similar assets in the old game and new on on 360 (based on what I've seen of 360 footage on Youtube which isn't making it look any better), it looks the same as the old game (which we have for 360). It looks FAR worse than the One version, but the One version is amazingly beautiful.
Though it's reasonable to think the 360 version might have been better than the cross-gen since it had been designed for only one system, I really don't think so. I think it's more a case of them noticing more now that a better version exists. This wouldn't apply to cross-platform games anyway. Now something like The Last of US for PS3, which was designed very specifically for one exact console and at the end of the generation, with effort put into using that console's power to the absolute max, might not be what you get from a cross-gen game, but then it's also not going to be what you get from a cross-plat game, period.