I think they could dodge a lot of bullets if they didn't call it 'marriage' but tried a different name like bonding, handfasting, pairing etc then allowing the same sex union.

I'm not against same sex marriage at all, but it'd kinda shy away from the stigma of folks getting their underwear in a twist over marriage not being shown in a traditional (to them) light.

Personally I would love to see same sex unions, as one poster mentioned earlier; there are a lot of people who play characters that don't properly reflect their r/l gender, so to leave them out of something like this based on aesthetic choice wouldn't be cool.