Looking at the path they took last year, the SE regional will likely be a week after the Texas regional (which is on May 28th). It's entirely possible they will concurrently have it along with the Georgia Force game that saturday; it's been a while since I've been there, but I'm pretty sure they wouldn't use the football Arena for VGC at all so they could both happen at the same time.That doesn't leave much time before Nats. :|
Sorry to everyone living in Florida, but it doesn't make sense to have a regional there. Nashville and even Atlanta are in the middle of the southeast, and cover an area roughly from Mississippi up to Kentucky/Virginia in terms of "closest regional". Florida, however, covers much less of the Southeast and is a much longer drive for those in the Carolinas/Tennessee and therefore doesn't make as much sense as Nash/Atl.
Assuming the Texas regional is on the 28th, we can probably assume that the southwest (possibly pheonix) will be the 21st, the CA regional the 14th, and the northwest regional (probably seattle) the 14th, while the southeast regional would be on the 4th and the NE regional on the 11th. However, this would obviously change on which locations are available and at which times, but I'm sure they have all that sorted out already.