5280AGL (cute name, sounds like a mile-high club, or something ) will become all RJ's within the next..
I guess you mean scheduled services, and from among the top two or three tiers of carriers, that is. Since below that level there'll probably always be some guys at airports like those offering not just charter but maybe even with scheduled services with Metroliner or Raytheon or Beechcraft-type commuter turboprops, probably on routes 200 miles or less, but maybe even up to 500 miles or less for more sparsely-populated parts of the U.S. like Montana. Also, I wonder if you consider a 717 a regional, or mainline jet. Since if its sales take off I bet you'll see a lot of those airports get served by it.
Having said that though, definitely RJs continuing to make inroads, they're deployin' 'em as fast as they can make them, it seems.