I don't know it this is technically feasible or not but wouldn't it be great if GOG users had some sort of multiplayer 'lobby' for some of its bigger titles? There is a great deal of marketing potential behind something like this if it could be done.
For instance to herald dungeon keeper into the lobby there could be held a competition with knockout stages on a couple of dedicated servers ($? of course) with prizes and perhaps trophies/badges that could be displayed in a
trophy/badges room/shelf linked to your account. Perhaps a ranking system. Imagine everyone playing empire
earth, total annihilation, duke nukem 3d etc against each other again. I would 'kill' for an old-fashioned homeworld (cough)(cough) match.

This has my full approval. Maybe a whiz-programmer could build a super-VPN-clienty-thingy for all GOGers to join. Like a super-hamachi or GameRanger, but specifically works with GOG titles.

If you're a premium user at Tunngle you can create two private networks with up to 255 people I think. Free version offers up to 30 people or something like that. I doubt it would be needed to have some kind of super-structure for it altough it would be kind of cool if there existed one.