Thanks to Jesse McGrew, there is now a system for same! See this announcement, which — despite the date and initial goofy front — is actually true. You can make yourself an account, create your own realm within the larger multiplayer world, and compose a game in Inform 7 that allows multiple players to connect and play simultaneously.
Yeah, really.
Emily Short's Interactive Storytelling 
I thought multiplayer IF was called “LP MUD”….
*scratches head*
What i would really like to see is an environment in which Inform coding can go on within the multiplayer environment, a la MOO programming.
Not sure how feasible that is though. Maybe the best I can hope for in the meantime is something akin to MOONedit.
Not feasible, assuming I understand what you’re asking for. Inform needs to be compiled.
Great! I posted that idea in the IF newsgroup once, but I did not follow up on it. It seems that somebody else had the same inspiration – and actually implemented it!
I hope that the library changes he made will be downloadable once.
Guncho looks really interesting but I don’t think announcing it on April 1st was such a good idea. Regardless, I think Guncho does deserve attention and am looking forward to seeing what kind of multiplayer experience can be created using it.