I wouldn't pay monthly for any game, if it just went to the developers. The only reason I would pay monthly for a game is to support the server, and keep it up so that other players and I could continue playing the game. People who think all money that goes towards playing online goes to the devs, you are wrong. Depending on the situation, it might go to devs. Like if you purchased a "membership" thing, like on RS. Some of your money goes to server, and some of it goes to devs. It's their way of keeping the server up, so they can make more money.
However... I wouldn't pay monthly for M&B. Not in it's current state. Personaly, BF2, I think you should just *STOP* posting/polling about multiplayer and start reading what other people think about it. Go in to some of the older multiplayer topics and look for it.
Also... not all of us are rich, and capable of paying for 5 online games per month like you seem to be. WoW? I can understand paying for that one. Some of the others, hell no. I wouldn't pay them a dime for multiplayer. I played Diablo 2 LoD for so long because you didn't need to pay monthly for it. All the major game companies are charging monthly fees now, and it's making it impossible for the less-fortunate people to play online games.
Honestly, multiplayer would be great for a completed M&B. But this game is in beta, and was not intended for multiplayer. Therefore, it wasn't coded to allow multiplayer to be easily implemented. THEREFORE... stop suggesting it. More suggestions about it will NOT make the devs have a change of heart and put it in. It will clutter up the forums, making all of the members irritated because they can't find the topic they posted in 30 minutes ago.