Actually the codeshare committee puts out a pretty good projection on what is happening with RJs, you'll find it on the DALPA site...

From the November 2011 codeshare committee PowerPoint presentation

Slide 3:
13 AC removed from Mainline fleet since the Aug 2011 MEC meeting

Slide 4:
8 MD90s added

Slide 9:
DCI fleet added 4 since Aug 2011 MEC report and 14 since the May 2011 report

Slide 21:
Peak DCI departures projected to exceed 60% of all Delta system departures in Dec 2013 before retreating again and reaching September 2011 levels by Sept 2016.

Again this isnt conjecture on my part, but the data presented by SM and RD of the DALPA codeshare comittee available at dal.alpa.org.

Cheers
George