[Sharlin]

I'm quite sure that such a major change in architecture will be completely infeasible by now. The whole renderer would have to be rewritten from scratch, and given how the Minecraft codebase appears to be a complete mess architecture-wise, the changes would probably reverberate everywhere.

[TazeTSchnitzel]

It's a real shame that when he decided to completely rewrite the Minecraft engine (which he finished but regretted), he didn't switch to using Modern OpenGL.