If the BEast expands, they're adding St Louis, period. They're the #1 candidate in almost every category. Fits the profile of the conference, solid market, solid on-court product, western support for Creighton, etc etc. And they're not moving from the A-10 to the MVC unless the Big East explicitly tells them they're not expanding for a very long time. But if they do, then we should press hard on them. Even if we have to take them with the knowledge they could leave us at any time, the short term gains and instability are worth it at this point.
Dayton is doable though. But in order for that to happen, you have to convince them the MVC is better for them than the A-10 for basketball. This can happen if St Louis and one of VCU/Richmond go to the BEast plus UMass moves for football reasons. Without St Louis, Dayton is the western outpost in the A-10. In the MVC, they'd be the eastern outpost. You'd probably have to let Dayton dictate who would be team #12 in the conference (maybe they'd want a 2nd Ohio school, or just best available basketball school, or who knows).