Trying to recall the FF1600, S2000, F500 F440, FV1200, and SoloVee1600 CM/DM/FM history (please edit/update as necessary):
CM (1990-1992) FF1600, S2000, F440, FV1200, and SoloVee1600.
CM (1993-1996) FF1600, S2000, and F440
DM (1993-1996) FV1200, and SoloVee1600
CM (1997-2007) FF1600 and S2000
FM (1997-2007) F440, FV1200, and SoloVee1600
Not sure when the F500 joined FM (2005?), so I neglected to included. I also do not know when FST1600 becomes FM legal (2008?).
Returning to Jim's question; Is it time to recombine CM/FM? I think not. From a participation point of view, FM seems fairly "healthy" at the moment. FM rule changes are being enacted to help the SoloVee1600(1950?) and allow the FST1600 which should help retain or grow the Vee based contingent.
A lot of work went into the creation of FM (i.e break out from CM/DM), so it's hard to imagine the FM competitors "welcoming" the FF1600/S2000. Plus, as pointed out above, CM would need to be slowed down (not something I favor!) to make this idea (somewhat) tolerable to the FM participants.
-pru-