I think same-sex relationships and marriage would be a great addition to the game. With dwarves, we're essentially building our own culture from scratch here. They're clearly not supposed to be based off of any real-world historical culture (what historical culture executed people with hammers, drank only alcohol, and lived underground?), and they're not really based off of any fictional one, either (what fictional dwarf civilization did all of the above, built pumps for magma, had perfect gender equality, etc. etc.?). Notions of gender roles and sexual orientation and even little things (my favourite--ancient Romans viewed pants as feminine) varied so much throughout history and between cultures that there's no real reason that, even in a pre-industrial society, a different species in a different world couldn't be more progressive than ours.
Arguing that humans in history in such and such location acted in one way or another is pretty irrelevant here. What matters is: what do we want our dwarven society to look like? We have an opportunity to make a society and culture from whole cloth, and I think we should take advantage of that fact. Dwarven males and females are equally well respected in all respects in DF, which is "unrealistic" if you only look at humans in medieval europe, so I don't really see any reason that they shouldn't treat dwarves of different orientation equally in all respects, which is also "unrealistic" if you, again, only look at humans in medieval europe. The world of Armok isn't the West, it isn't medieval (It's not set after a continent-wide empire collapsed. The world starts the way it is in dwarf fortress), and, obviously, it's not even humans we're talking about here.