You might be surprised just how much you can rewrite of Blender's UI if you want to.
replyAnd you get battle-tested software and a huge collection of existing plugins, operational modes, export formats, all that. Fully bespoke software for everything you want is a way toward losing interoperability between people and platforms.
It doesnt have to be one or the other: you can have custom software that still works within existing/interoperable formats, as I’m doing here (im not planning to reinvent OBJ/FBX/BLEND)
replyBut building up as opposed to building down or rewriting is freeing.
I can pull in ideas from Houdini and mix them in. I can use Blender’s source as reference for specific implementations should I need. I can keep my tooling specific to the projects Im working on and design it to fit that as opposed to build a workflow within a software meant to be general purpose.
IMO, this kind of full customization is going to become far more commonplace.