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)

But building up as opposed to building down is freeing in that I can also pull in ideas from Houdini and mix them in. Not to mention BECAUSE Blender is OSS, i can also use it as reference for implementations of particular things should I need that too.

IMO, this kind of full customization is going to become far more commonplace.