It needs a huge update in general. Make the UI look better, remove these weird object limits, allow the texturing of objects, stuff like that.

Some random UI ideas that might be helpful, dunno:

There could be a tab that, when you click things, will fill with data about it that you can change. If I click Tori's left hand, it'l fill with data like it's size, scale, et cetera in it's own little tab. If I click something else, it'll overwrite with the other things data. If I shift click something else, it'll open another one of these "dynamic" tabs with that ones data.

I don't know if this is a thing, but some form of lua scripting on objects/joints would be super. Something like a global variable called "this" or something that you can change depending on whatever. Maybe a couple functions that you can hook in, like an on-update (every frame), on-start, on-collide, etc. Would be super awesome for more dynamic mods, like making a mod that could spawn and shoot a bullet out of a gun every time the holder holds their wrist.

There could be plenty more ideas, would love for this to be expanded on, but in general - the mod maker should be updated.