All of that is irrelevant to an end user. They have the choice between tool A which is free but developing very slowly, or tool B which is paid but has all of the stuff they need.
99.99% will choose tool B and rightfully so.
Case in point: Serif isn’t currently rewriting their old stuff, they already did 10 years ago. Affinity photo/designer/etc have been out for a decade.
My point is that if you want a future-proof software, you need a solid code base.
Affinity already fix that. Clip Studio Paint done that. GIMP dev is currently working on it.
Regarding Shape Tool: this feature is dependant on Vector Layer. The earliest attempt to implement this is back in 2006: https://web.archive.org/web/20061219233008/http://lunarcrisis.pooq.com/wiki/Gimp/SoC2006Log
I recommend to check the discussion for Shape tool and Better vector Tool here: https://gitlab.gnome.org/GNOME/gimp/-/issues/11190
If you check Gitlab repository of GIMP, they’re actually rewriting some old-codebase to be more future-proof. And that works really takes time. https://gitlab.gnome.org/GNOME/gimp/-/commits/master
A lot of major design software are actually doing this. For example:
You cannot just slap new feature continuously. The software will end bloated and slow like Photoshop.
All of that is irrelevant to an end user. They have the choice between tool A which is free but developing very slowly, or tool B which is paid but has all of the stuff they need.
99.99% will choose tool B and rightfully so.
Case in point: Serif isn’t currently rewriting their old stuff, they already did 10 years ago. Affinity photo/designer/etc have been out for a decade.
My point is that if you want a future-proof software, you need a solid code base. Affinity already fix that. Clip Studio Paint done that. GIMP dev is currently working on it.