I'm surprised this needs saying but doing that is a mod in of itself. Not just any mod, but the biggest mod in any game ever. You realize you'd have to make an hdl environment from scratch right? I can't even think of a way to express how much work that would be. That's xilinx ise (a 20 gig download) without the IP libraries and less real world constraints. The compiler would also be insane.
Just use computer mods for things too complicated to practically accomplish with a few gates (MSI and up).
i think the most space wasted in HDL environments is mostly the architecture of the fpga/cpld for the routing. Interpreting vhdl itself shouldnt be that hard given a human can easily read it^^ Minecraft wouldnt have to rout logic, it would just have to interpret it... idk
edit: i think for reference we should rather look at hdl simulators...