Depends on launch date.
PS3 to PS4 is some 8x jump (10x according to some devs). If PS4 to PS5 is about the same, which is to be expected if it launches in 2018/19 with this slow progression of node shrinking, then I don't see native 4k as option due to pixel count.
720p to 1080p is 2.25x more pixels, 1080p to 2160p is 4x more pixels. They would need much more than 8x jump to make up for resolution penalty and keep same relative jump as in 8th gen.
So, if they launch in 2018/19 with 8x jump, I can see anamorphic 2160p with good upscaler as an option.
If they wait bit longer, or something really changes and 7nm node is mature and relatively cheap, then sure, native 4K might be achievable at $400-$450 price.