The A10 is not going to take any schools west of St Louis until it is sure that SLU is staying in the conference. If SLU and, to a lesser extent Dayton (UD), leave, the A10 will have lost ALL of the schools on its western side (SLU, UD, X and Butler). They aren't going to grab WSU and make all of their member schools travel all the way out to Wichita for one school. Besides being a huge drain on resources, it just doesn't make any logical sense.
On a related note, I feel that Bradley would be more appealing to the A10 than WSU merely because of proximity. Of course, if both UD and SLU leave the A10, Bradley would be in the same position as WSU.
Ultimately, I do NOT think the Big East is going to take both SLU and Dayton. When the Big East adds two teams in a year or two, they will take one team from the west (either SLU or Dayton) and one team from the east (Richmond or VCU most likely) to make clean east and west divisions. While I think the Big East will select SLU over Dayton, I think the MVC's best opportunity would be if the Big East picks Dayton. Despite SLU's desire to have an eastern presence, if they are the ONLY western team in the A10, it is pretty unlikely they would stay there and the MVC would be a great fit. If Dayton is the school left behind, I think they are far enough east that it doesn't present the same drain on resources to remain in the A10 as it would for SLU.