A System Shock tabletop RPG wouldn't have enough of a setting to be worth the effort and hassle of dealing with the setting being copyrighted. You might as well just develop something cyberpunk with a few similar history elements and call it good. Especially where there weren't any survivors to speak of from any of the SHODAN incidents, so it's not likely to be part of the official histories anyway. Looking at the new steampunkish things for Zweihander that are coming out in Main Gauche, I'd say it's reasonable to just assume it pretty much is the same setting as TDM. The technology level is roughly the same except that Zweihander includes primitive firearms (Which might actually be an interesting addition to TDM if implemented correctly). And the major factions of TDM are similar enough to some of the factions for Zweihander that the minor differences could be easily plastered over and ignored. Any TDM cities would likely fit right into a Zweihander campaign with little to no modification. So if you want to develop some tabletop adventures in the city of Bridgeport using the Zweihander rule set it would probably work out pretty well, hammer-wielding fanatics and all.
It's not a bad idea really, but the play styles are different enough (single-player thief vs multi-player party that may or may not include a thief) that there's not going to be a lot of overlap potential in the storylines. So at that point all you've got to share is overall setting. That said, a forum section for discussing non-TDM uses of the setting to help keep them all consistent and reach consensus on what lore should get added to the wiki might be an interesting idea. Some world building from points of view other than a sneak-thief would probably help flesh out the world quite a bit. (Note that this post caught my eye mostly because I play quite a bit of low fantasy tabletop, so if there is a community here interested in expanding the lore via other game types I'd be happy to contribute, but there are probably few enough of us that we'd need to agree on where/how to collaborate.)