Someone should strip this and turn it into a generalized graphics engine similar to OGRE or suchlike.
The problem with this sort of release, if you can call it a problem, is that if you are going to go to all that effort to make a game, you would probably want to sell it and so from that perspective you are probably better off writing your own or using something with an end-user license. Although I'm sure you can license it from id if you wanted to.
The main interest from this is as reading matter-- it's always been fascinating to see how Carmack coded things.
Even back to the Doom source, it's always interesting to me how brute force Carmack's coding is. He doesn't try to do anything fancy or elegant. His stuff is always in a very simple style and fairly easy to understand except for the core engine math and "black magic." He engages in a lot less of the fancy dances that a lot of other coders do.
