That depends. The Knuth MIX architecture is much like the architecture Notch has in mind. But the more recent MMIX architecture is far more like a modern 64 bit RISC system. In fact, it does look odd that Notch would prefer such an old behemoth nowadays.

An MMIX like ISA would open up the world for compilers much more. With this, it looks like people should be confined to writing simple stuff - which is kinda the point but still rather sad.