what licensing issues?
Mojang needs to change their stuff into bytecode with runtime environments if they want to secure the engine and fight client side modding.
Due to the MCP, I can decompile the whole client and make it do whatever I want in a server game. I haven't put effort into it because if I was going to work on game code, it would be WF4 and not minecraft.
even obfuscated, java jars are not the way to distribute a paid for, networked game. ever.