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I do think they will wait for 7nm fabrication process with high yields so the console can achieve a decent unit price with great performance. We debate when commercially should be right for the console but it wouldn't surprise me if Sony weren't more focused in releasing when they can achieve their hardware goals to make a next gen product worth having. I still think a launch between Autumn 2019 and Autumn 2020 is likely or at least quite possible.
It's possible we see some new games released that are ps4/ps5 compatible for a while but unlike xbox one x there will be exclusive games making full use of the ps5 hardware that gradually appear until they become the majority. The PS5 will probably be powerful enough to do full PS4 games in VR without compromise. It wouldn't surprise me if many classic ps4 games go VR and the VR experience will be improved on PS5.
I don't think people need to worry about ps4 it will likely to continue to sell at high numbers even after the ps5 launch.
It wouldn't surprise me if we got a ps4 without optical drive and with flash memory instead of hdd in a budget set top box that enabled people to play ps4 games natively as well as stream ps5 games either from a ps5 you own or simply over psn from server streaming ps5 systems. Sony makes it's real money from psn and ultimately it wants as many people using psn as possible and buying services, product from it.
Whatever the timing we know Sony will be working on a ps5 no question. Late 2019 is probably the earliest possible for release, maybe 2021 is the latest possible realistically so I don't see the big deal it will happen within a window of perhaps 2 years.
