It'd be a sledgehammer approach if they disabled entire nameplate customisation beyond tweaking available CVars
As I explained earlier, there's no way to programmatically determine what a texture is supposed to do. That's something we, humans, decided.
As an SE in general, and addon dev in particular, I think that collateral damage doesn't matter, prevention of undesired behaviour > customisation. That's why we have various SecureTemplates, that's why Blizz code can be "tainted" by 3rd party code, that's why we can't do many things from Lua while in combat, and that's why we can no longer customise friendly nameplates in instanced PvE.
In Vanilla, when we had none of these restrictions, and we even could replace stuff in "\FrameXML", well, it's possible to mess w/ those files, but it's bannable offence now, kek, it's REALLY easy to create a one button UI that would toss everything under your cursor, alternatively you could create one smart button for all actions/abilities