> Honestly, with the first step, it seems the PMs are already halfway there to implementation of the feature so I wonder if in the future they'll just do everything themselves and a few devs will be around as SDETs rather than full blown implementers.

Judging by every PM I’ve worked with, 0% chance of this happening. Much sooner would see SWEs making PMs redundant than the other way around. Unless of course you want a system that falls apart like a house of cards as soon as you get a single user for your vaporware.