Look for the Delta 135's to go away next year (official already, buyers found for all aircraft), and the American 140's to go away within 3 years (based on eagle's ability to cover the flying). That will leave 8 US Airways 145's and 7 United 145's which can easily disappear during the annual reductions in flying after summer (probably in 2008). The Delta 145 and Continental 145 fleets are large enough that any reduction will take time... I would guess that any 145's reduced from the Untied, Airways, and Delta sides would be sent to the Continental side to replace the CRJs as soon as those leases expire. The Delta and Continental flying is still profitable for CHQ, and will likely remain for a few more years to help finance new 70+ seaters. Bedford has definitely said he wants out of the 50 seat market, but I don't think he would go so far as to sell off the CHQ certificate just to rid himself of the 145. The 145s are his leverage for negotiating addition 170/175's, and I believe that the rate of acquisition of new 170s will dictate the rate at which the 145s disappear.
Originally the 30 175's ordered were for USAirways flying, and were to replace 20 145's for a net growth of 10 aircraft on the Republic side. Then Frontier announced we would fly 17 170's for them, four of which would be coming from spare aircraft on the Shuttle America certificate... net growth 13 170's. Soon it was announced that eight 170's from the 28 original (Mid Atlantic) USairways 170's would be sent to frontier and 8 new 175's would replace these 170's on the Airways side for a net change of 0 in the Airways fleet. The purchase of the 8 new 175's was never announced, so you may infer that 8 of the 13 175's mentioned in the press release were already expected, leaving 5 new 175's in the press release that have no announced home yet. Or, perhaps all 13 are new (the 8 needed for airways were just converted options not worthy of a press release) and are headed somewhere yet to be named.
For what it is worth, Frontier has yet to come near 17 airplanes in service, and only 11 of the 38 175's for Airways have been delivered, so a new aircraft order for either of these two code shares is unlikely. United has not expressed a real interest in growing the 170 platform, and scope would limit new aircraft to 170's not 175s. That leaves Delta, who is growing their large RJ portfolio, and with whom we expect an increase in flying on large RJs as a trade for the loss of the 135's (Bedford's goal has always been 1:1... 13 175's for 15 135's would probably be an acceptable trade in his eyes).
Of course, Compass hasn't started flying 175s yet, and we all know how much Bedford likes buying up wholly owned subsidiaries...