openGl is supported awesomly, as well as X11.
multiplayer is pre-scheduled and verry clean and efficient, but it could at-least be changed so an external server can be started and players are allowed to join and leave without the server quiting. (CSDoom was awesome, but some l33t crax0r made some code to crash the CSDoom servers and thus the port became stale because of lack of skill and effort to prevent the crax0r from doing so.)

Perhaps, the only thing that can be done to prboom is to create a graphical user interface so it is easy to start a game, start a multi-player server, and sniff/join an existing multi-player game. Besides those, this Doom engine has the best support for all the hundreds of flavors of doom engines that existed and have been assimilated. I highly recommend as a download for any and all people; even the shareware gameplay is fun!