After reading the basics thread over at SRK and playing through the tutorial of BBCS with type B (I think), it seemed similar in premise to me. I mean, yeah, BBCS has all the barrier bursts and negative states and counter hits and shit and MvC3 has fly/unfly and assists and snapbacks and whatever which don't parallel at all. But in a much larger picture, BBCS (and BBCT for that matter, most likely) when set up with type B have the combo system that generally works as A cancels into B cancels into C cancels into D cancels into special. MvC3 operates, as I understand it, on a light/medium/heavy and (launcher/air exchange) control; and light cancels into medium cancels into heavy cancels into launcher/exchange. So it's that same A > B > C > D premise, where there are no kicks or punches specifically, just attack strengths that cancel into stronger and special moves that vary based on input motion and strength pressed. It's not a "oh shit, it's exactly the same" or even "

me, they borrowed a lot from BB"; but to me the MvC3/TvC system (in reading, since I've not played TvC) reminds me of what I learned about the BB system during the tutorial in a fair number of places. They also use super jumps and jump cancels and dash/airdash (most characters at least) so there are a lot of things you could probably pick dealing with MvC3 by learning BBCS if you're relatively inexperienced with fighters.
Of course, you'd also need to be familiar with MvC2 so you know about all those things that are different as well as the general feel/speed of an MvC3 game. But if you're used to MvC2 and the "magic series" and trying to figure out who has what launcher/etc. I would think that playing/learning the basics of BBCS might help prepare you a bit for the new button layout/system in MvC3.
When I mentioned in the FGT as a musing, I was asking if anyone who played BBCS and MvC3 thought the new button layout and general comboing rules were similar and I got chewed out and laughed at. But the more I play around with BBCS the more I think it is similar is some basic general concepts to the new control scheme for MvC3. I could be totally off and drawing the wrong conclusions about it all, but I'll have to wait another 4 weeks to try it out and see.