I don't understand what Sony and Microsoft are doing. The drop to a new processing node for video cards and the move to HBM2 is coming at the perfect time to make a new full powered PS5 and Xbox 2 in fall 2018. Just wait 30 months and do this right and return to a proper five year cycle. All these incremental upgrades and semantic arguments about what to call it make no sense. Just jump to the new gen on schedule.
It seems you don't understand developers needs.
The more significant the difference in power, the harder it is to scale. A full powered PS5 and XBox 2 in 2018 means a few things to developers.
1) Drastically cut down the vision of your title in order to accommodate PS4 and PS5.
2) Cut off a large existing market by target only the PS5.
3) Skip out on PS5 til a large enough user base emerges then jump in still leaving money on the table.
4) Smaller titles are mostly fine in this scenario.
Something like a PS4.5 helps smooth that transition out. The scenario changes to:
1) Accommodate PS4.5 when making a PS5 game. The lesser gap means the scale of the title should still be attainable. It may not perform nearly as well on the PS4.5, but the game doesn't have to be complete reengineered nor does the vision have to be cut. Put some notice that says playable on PS4.5 and PS5.
2) Smaller titles are mostly fine in this scenario.
3) Target only PS5 due to the same reasons that some PC games only target 980s and the like. Your engine is scale-able but you just want to target the bleeding edge cause its cool.
4) The PS4 lifetime is probably extended into 2021 or later so the user base continues to expand.
The second scenario is much more preferable to developers.
