Let's not all panic at once here...
If you understand all the issues and dynamics you'll see that there are major obstacles to regionals operating jets with more than 76 seats(or 90 in a few cases). Think carefully...no US regional/commuter that I know of has attempted to operate mainline aircrfaft since the advent of the RJ (with one exception).
There are three ways this could happen:
A) A stand-alone branded operation. Reason it is unlikely: Might work on a small scale serving very limited niche markets which do not compete with a major partner. This is what Xjet is trying to do, and they may be able to pull it off with small ERJ'S. But if they try it with anything larger, it will be VERY hard to find markets where:
1) They don't compete with CAL and/or DAL. If they do this they will get fired, and will lose their REAL source of income. Most regionals have two or more major partners, which makes it hard to avoid stepping on somebodies toes.
2) They don't compete with SWA, because theywill get their @ss totally kicked. If you think you can operate a narrowbody somewhere, SW is already there waiting for you
B) A traditional regional-style pay-for-lift agreement (like RJ's but with bigger planes). The reason it won't happen: Scope prevents this, and hopefully the big boys have wised up and will hold the line. I think they will. It would be nice if big t-props were better accounted for, but ultimately they are slow compared to a 75 or a Bus and would not be used for long-range service.
C) A combination of the two...a branded operation functioning as a code-share with a major partner. This almost happened with mesa and legacy Airways during the BK proceedings in 2003/2004. JO wanted to operate "branded" 737's out of PIT with a US Airways "codeshare". They were going to use BK to get around scope and sell it to the judge as a "codeshare". Mesa alpa refused to fly 73's for RJ rates, so JO backed out. This is hard to accomplish because you still have to get around scope, which allows legit codeshares but would not sit still for regional lift disguised as a codeshare.
Look at all of the recent narrowbody entrants: JetBlue, Virgin America, and SkyBus...all start-up operations who had no pre-existing industry relationships.
Regionals operating bigger airplanes is not really something to worry about. I'd spend more time worrying about Virgin & Skybus, but the good news there is that it's REAL hard to break into the mainline business (see JetBlue). You are going to blow BILLIONS of dollars for a historical 1% chance at long-term success.