Super interesting! I'm curious what the purpose is, though?

Edit to answer myself: Looks like this is more of an offshoot of the FreeHL projects by the same author, which rewrite GoldSrc game logic to QuakeC to get those games to run on open source engine stacks, where the utility is more obvious. I guess it was just fun to see how hard it'd be to get HL2 content running.

A bit similar to the OpenMW project working on Oblivion and Skyrim content loading on the side, though perhaps that's a more obvious future vector for that project.