Mixed feelings. I played M&F earlier on (so much might have changed). M&F seemed to move too fast for my playstyle though.
The codebase in BM *is* quite legacy. I do like the ability to adjust maps in M&F. BM development isn't in the best shape, and documentation even worse. I've been trying to informally share how different BM components influence each other without giving up algorithms. So the sound of M&F's APIs and improved structure sounds nice.
Advies, priests, and infils aren't really the core of BM, so while I absolutely love the priest/ambassador combo, I'd understand. Features I'd be concerned for missing in M&F are the government systems. Not just republic/monarchy/theocracy, but all the individual settings, the existence of council positions and their respective buttons, the various secession, rebellion, change allegiance etc. buttons. In essence, the political side. Another aspect i don't recall in M&F (which very well could exist now) are the battle nuances of unit settings, marshal settings, and such.
I realize many of the things, largely unmentioned here, I prefer in BM are aesthetic so I feel those are less important in the big picture, but it does incline me to a preference for BM.
My general, overall thought is that there *is* a dedicated group of BM players (probably ranging between 50-100 players) that wishes to continue BM and not M&F (or they'd have joined already). I strongly believe we have too many islands and realms for the current playerbase and this results in whatever new players *do* join predominately finding boring, inactive realms. And, until a recent movement by various players across EI, BT, DWI, wars were primarily between large behemoths with large marching times. These are only worsened by having reduced noble character limits to two characters from three, meaning less opportunity to get a good realm. And then again, by allowing advies to be played from the beginning, confusing the poor new player away from the main core of the social game and into a quiet, deserted corner. Thus, I think reducing the playable landmass and adjusting character limits is important. However, while I think this paragraph is relevant for consideration in Tom's suggestion, I strongly encourage further replies to not focus upon island-sinking in this thread, as it would detract from the core of his suggestion. To continue, even if a merger is done, I think that dedicated group of BM players will strongly desire/pine/yearn for a level of 'oldschool' BM, even if its only 1-2 smaller-sized continents.
EDIT/ADDENDUM: Also, in copying continents I would worry if there is enough playerbase in both M&F and BM (and there's likely significant player overlap) to cover all the regions. Would continental regions be reshaped or continents shrunk in square mileage?