I'll go out on a limb here and say that that's unlikely...
I would imagine those aircraft to come within the next 2.5 years.

Here's why:

The only way for Delta to increase the number of 76-seaters is to remove 50-seaters.
The recent 40 CRJ900 order was in exchange for returning 60 CRJ50s back to Bombardier. At that exchange rate the 717/CRJ900/CRJ50 swap out is unworkable as negotiated and thus additional ways of getting out of CRJ50 leases are needed...
Adding about two dozen new but current generation narrow bodies in exchange for getting out of the 50-seat leases provides an additional path to reduce the CRJ50 count...
Additionally the capacity purchase agreements with the DCI providers will need to be reworked. To do that, current CRJ50 providers will need a carrot. A 1-t-1 swap of CRJ50 for new CRJ900 is most likely the only way they will agree to terminate the current CRJ50 CPAs.

The whole transaction hinges on the 717 to 76-seat to CRJ50 conversion formula. The last 717 will join the fleet by 2015, so it's likely this rumored transaction will close in the same timeframe.

Cheers
George