It would be really weird to have to buy both versions as you are already paying for 99% of Animates features if you are subscribed to C3.
It also would be bad UX to have to switch between almost identical software depending on what features you need and there wouldn't be a version where you actually can do all in one. Also because of the removal of features it's even worse, let's say I want to bake a trail from the 3rd party addon Trail Renderer, would be impossible afaik.
It's especially weird as the removal of the features is purely artificial.
I also don't think that adding that feature to c3 would make less people buy Animate, maybe it would mean more people buy c3 instead of animate tho, as now there is a version that actually does it all.
I don't think it's a good deal to make people buy a second identical house with a refrigerator if they want a refrigerator in their house. Obvious hyperbole, but I think it's clear what I mean.