Eh the difference between 900p and 1080p isn't that massive sure it's not ideal but with a decent upscaling, it's not as much of a night and day as 720p to 1080p and this is with a computer monitor so it's far easier to notice the issues compared with a tv.
Certainly worth the increase in framerate, to me at least.
It's "massive" to me. AC4 pre-patch at 900p was immediately noticeable. And it is very, very easy to notice the issues on my TV. Assuming that a monitor would be more noticeable is a bad assumption. I don't sit 10 feet away from some little 42" screen. I sit 8 feet from a 60" screen and you see every little tiny thing.
It wouldn't ever stop me from buying it, but I will notice the upscale blur every moment that I am playing it. A resolution patch is wishful thinking, but hey, there's always a possibility of it being optimized better at some point. I just hope this doesn't become common.