From an official source.

• The four-year CPA is for 11 CRJ200 aircraft flying under the American Airlines code beginning January 2013.
• All 11 aircraft will shift out of our Delta Connection program beginning in November 2012 to start transitioning to the American operating and paint specs.
• ExpressJet will begin operating five aircraft under the American code in January and six more in February 2013.
• ExpressJet’s American schedule will be concentrated out of Dallas/Ft. Worth (DFW), where we plan to open a crew base and a small Line Maintenance operation to support the service

Hope it's true! That's gonna go ultra senior

"These 11 CRJ200s will be ExpressJet aircraft flying under the American Airlines code, with the American Eagle name."

Crazy. Guess AMR owns the name and is changing how the business model works.

Is there any odds of a new hire class being started to fill the new dfw base?

No, this is not growth. It's just a transferring of planes. Hiring for attrition only

Plus, the DFW base will go very senior

The fact sheet on the company website said that this announcement itself wouldn't lead to more hiring since this is just a shift of aircraft that were being retired from the Delta operation.

Sorry to hear this. I'm sorry for the hard working pilots at Eagle who are seeing their flying erroded.

But how does this effect the total picture with some of the 200s going to new flying with the larger RJs coming online as well soon?

SkyWest, Inc +34(DL) -66(DL) +23(AA) = -9

Assuming everything is split close to even, ExpressJet is gaining 0 aircraft; losing 5+ by 2015.

Yes, the joy of possibly benefitting from another's loss is still alive and well in the airline pilot profession. I understand you may say you didn't mean it like that, but isn't it interesting that's the first reaction ?