Mojang already announced that "deep modding" won’t be supported. They’ll extend the stuff current resource packs can do, but they want to avoid modders replacing or extending any game mechanics directly.
For example, modifying the rendering pipeline will be impossible.
What modders expect: Minecraft as a whole engine, similar to the API Unity presents to developers.
What Mojang is willing to deliver: A modding API that’s glorified command blocks.
he seems to be okay with deep levels of modification, and even says that things have been abstracted enough to potentially support it.
He merely says that nobody has written it thus far with that consideration in mind.
Any chance of modders swapping to an opensource minecraft clone?