Denver is too far, as is UT Arlington, and neither school is all that great. DBU works well for baseball, because they are a baseball-only school, and a really good one that adds value to the league.
I think most of us agree on Murray State. Beyond that there aren't a lot of good options. Oral Roberts is probably the best 12th option. Besides their run this year, they have a history of actually being good, particularly in the first decade of this century, and they spend like an MVC school. And believe me I'm well aware that the ORU haters will come out in full force.
You could make an argument and say that if Belmont is under consideration, then maybe ETSU and / or Chattanooga should be too. However Tennessee is probably just as far from Iowa as North Dakota is from Illinois, so there's that.
I've actually never understood the fascination with Belmont. I follow the OVC so maybe it's because I know them better. They are good, but they have no fans at all and they play in a city that couldn't care less about them. My fear is that if they are ever not good, they will be a major liability down the road. The fact that they have turned down the MVC twice should tell everyone all they need to know about them. If they played in the MVC, I also believe that they wouldn't have the gaudy and often deceptive records they have (that also includes Murray St). Playing on the road at UT Martin or SEMO is a lot easier than playing on the road at Illinois State or Bradley. I'm a big OVC fan and I enjoy their hoops, but facts are facts.
For what it's worth I'm to the point where I don't really care if we expand or not. No one out there really excites me other than Murray State and the two XDSU schools that will never be considered.