These aren't two radically different pieces of hardware like the PS3 and PS4, it mostly looks like a bump in graphics capabilities.
It seems fairly plausible that games will run well on the PS4 in HD and on the new machine at 4K.
I have a PS 4 and am not particularly worried about this. Maybe if the VR is better with this on or if I decide to get a 4KTV at some point it might be worth the upgrade.
Otherwise I expect to be happy with my PS4 and expect a lot of people will still continue to buy the cheaper PS4 because they only have an HD TV which will keep the PS4 as the most common PS4 platform (and therefore the one game makers consider the primary target) for quite a while.