I wouldn't be surprised if consoles follow a more PC-like upgrade path (or would 'smartphone-like' be more accurate?). A few years ago I would've never believe a console would need to 'install' a game and consoles would forever be 'place the disc inside and play), but they all require installations now.
I really don't think smartphones are good example for getting good games. Top end phones are under-served, bottom end phones get crushed by requirements. It's aim for the middle an hope it works, really a mess.
If I was a Developer, I would just ignore any PS4.5 because most of the market would be PS4.0, and the PS4.5 would be backward compatible anyway. Given that Sony releases a new PS every 6-7 years, that is 2019.
The only thing I can see is they pull PS5 a year early in 2018. Should be able to do console 4K by then (maybe).
IMO PS next is 2018 at the earliest, and it will be a PS5, not a dot release.