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:
- Manga Studio -> Clip Studio Paint. CSP is now “de-facto” software standard of comic industry, including webtoon. Hugely popular in Asia.
- Serif PhotoPlus -> Affinity Photo. It was regarding as the best Photoshop alternative with arguably easier interface and better performance.
You cannot just slap new feature continuously. The software will end bloated and slow like Photoshop.
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.