mersk862 has done an excellent job of analyzing what is sure to be one of the more complex combinations.
I thought there had been some talk of the DL shuttle moving over to A sort of like at LGA, but I guess they are trying to keep it all together. If the shuttle moved, is there enough transfer from the shuttle to mainline to require an airside bus?
I also can't imagine CO moving -- their club is the classiest at DCA -- the old restaurant of the historic terminal.
I'd also heard that NW's lease on terminal A is very favorable, acquired when from Eastern or US during the first round of airline bankruptcies?