This reply kind of also touches the other recent polls...
I play almost exclusively dwarves, and have tried the kobolds back in 2012, but it didn't do much for me back then, maybe because I was too inexperienced back then, even more than now. I haven't tried the last couple versions of MDF, but after seeing a video of the warlocks, I'm sure it's going to change this week, and after reading about the gnomes I'm really interested as well.
I think the main thing that stops people from trying the other races is the lack of more knowledge on how things work, how things differ, which goes hand in hand with my vote for both improvement in the manual and the online presentation. But I think that for only one person to do this is really bad, It's generally a more boring job, that can get even more boring doing a big chunk of it, specially from you, that could be actually improving the mod.
My suggestion would be to move everything to the MDF wiki, and link people directly to there, and thus encouraging them to share their knowledge, or even make it more presentable. Also, to kind of kickstart it, make kind of a 'task-force', making some people initially 'responsible' for each race, so volunteers would write more about the races, including manuals and whatnot.
And lastly, since I already went over the topic mains poll already, just to let my support for the addition of the human race, and say that the prospects 'Humans Ideas post' look absolutely amazing. Also, strongly encouraging the above ground fortress making building a bit faster and mining much slower would be awesome.
An idea, though I'm not sure if possible to be implemented or not, but I'm still going to throw it out, is to also incentive the mining in the form of a big quarry. Mining an subterranean tile would be painfully slow, mining stone marked as 'above ground' would still be much slower, but not as much as the subterranean one. This should lead to super interesting scenarios. I'm have a bunch of other ideas right now, but I should go to the specific thread..