As you've probably noticed there are four stickied thread and a new version of DoomRL today. This is obviously not a coincidence.
The mod server is a new addition to DoomRL. Its main purpose is to save you, the player, from having to go through the agonizing task of downloading entire mods and dumping them into the modules directory. Now DoomRL does that heavy lifting for you (though nothing is preventing you from doing it manually anyway).
The mod server's content is currently limited. Only four mods are on it and three of them were originally included by default. Generally speaking mods should be relatively feature complete and stable before they are added; there are no formal guidelines since the modding community is small and everyone knows everyone else. I for one would like to add Tehtmi's wonderful works to the server ASAP; after that it is anyone's guess.
I would like to propose each mod on the server have at most three threads--one for the source (if released) that is kept pristine, one for bug reports, and one for general discussion. That should keep things clean without drowning out newcomers to the modding arena, and if not we can restructure a bit. And I guess that leaves this thread open for active discussion about the mod server in general. Get playing, slackers! The chaos gods demand blood.