I can't imagine the SDK ever being flexible enough to allow addon devs to provide solutions like e.g. changing the FOV, because if Scirra puts the time into it they might as well simply add that feature themselves.
Or the ability to control the sampling mode and fullscreen scaling quality on a per layer basis. So many times I wanted to have a small scale render for automatic pixel perfect visuals and low cost for effects but also needed a high quality HD render for readable text.
There will never be an SDK flexible enough to providing these things that can't be worked around with other means and that Scirra would never add themselves if I made a feature request for it.
I'm not great at art and for me it opens up a whole host of projects that I put on ice because I wasn't able to use that art style without readable text in game and for menus.
If they obfuscate all internals, those (and future) solutions to my problems are simply gone, Scirra wont provide them, SDK wont fix it.
And for what, for the possibility that it might stop working in the future?
I rather have a period where a hacky feature is working than it never being available for me at all.
Every commercial game eventually sticks to one C3 + exporter version combo anyways, and that's not just a C3 thing Unity, Godot, Unreal, every game developer does this.