Hopefully the base PS4 gets bumped up. I don't see any reason why it would be 900p, unless the dev wants the game to be completely locked at 60fps 100% of the time.
Hopefully this doesn't start a trend where developers get lazy and just leave the base PS4 version at "good enough".
Lazy devs again huh? You are not a dev, why do you assume it must be able to bumped up?
Your concern will never happen as base PS4 still sells a lot more than the Pro.