The bottom line is the dollar. The regional airlines hit their peak a few years back, and since then momentum is trending downwards. As much as people want to complain about meager wages, it's somewhat of a self-correcting problem. There are signs that this problem is going to be catching up with the regionals -- their business model is going to have to drastically change at best.
The "pilot shortage" is a shortage of qualified pilots -- not at the top tiers, however. There is a shortage of pilots willing to work entry level jobs because of barely livable wages (especially for those with families to support) and no guarantee of significant upward career mobility.
I am a dual-rated guy and currently fly helicopters for Uncle Sam, but even in the rotary-wing side of the aviation house, there has also been a looming "pilot shortage" for years. All the Vietnam-era pilots are allegedly 'on their way to retirement,' yet what we're seeing is a surplus of qualified military helicopter pilots from the Army, Navy, Marines, Air Force (and USCG) getting forced out of the military and taking jobs that low timers and civilian-trained guys are fighting to get. Needless to say, there was never a true shortage because there was a very qualified person ready to step in once there was a vacancy.
I digressed slightly, but my point is that if anyone thinks there is going to be a shortage at the major airlines, joe pilot with his ATP-R is not going to walk into a job. It's going to be competitive at the highest echelons (as it is in any industry). The shortage is going to be at the very bottom. The good news is that it will force the industry to make changes that may make working an entry level job at a 121 carrier more desirable; however, it may take some time... how much times, who knows, but I wouldn't count on it any time soon. It's a slow, slow bleed...