If you build it, they will come. There is a well-established and respectable group of posters on the forums over at Laxpower that would welcome another place to express opinions, etc. I know of a few who already frequent both these boards (for football and basketball) and laxpower.
The lacrosse community is probably the most vertical community in college sports. That is to say, a real college lacrosse fan knows as much about Salisbury or Middlebury as they do Maryland or Syracuse. There is a general respect across divisions which doesn't exist nearly as much in the other sports being discussed - in large part due to the great lacrosse traditions established at many Division III schools, some of whom used to play against "the big boys" before the NCAA sponsored the sport.
There are other discussion boards for lacrosse, but laxpower is the only current one with ANY sort of real moderation and organization. (I'm looking at you Inside Lacrosse and Lax.com!) I think a lot of the regulars over there (and a good deal of newbies) would appreciate the features of this board.
After lacrosse, from a purely national level, track, softball, soccer, and volleyball make the most sense. I just don't think there would be as much hardcore interest in the Division III levels of those sports.