For those arguing about taking away resources from single-player, here is how it actually works. Example:
Bioware comes to EA and requests 50$ for the Next Mass Effect, as your good old standard Mass Effect game (single-player only)
Later in development, Bioware says to EA that they could put in a multi-player mode into the game that would diversify its appeal to the audience and generate extra income through micro-transactions and would keep a larger portion of the users around for longer instead of just beating the game and returning it (the casual fans that make up about 50% of all people who buy games)
EA approves of the idea, grants Bioware an extra 25$ to make the multiplayer component.
So, as you can see, the budget is not 75$ total - 25$ for MP. It's more 50$ for SP + 25$ conditional for MP development. Bioware would never get that money if it weren't making an MP component.
And while I agree that tying multiplayer's readiness rating to the single player campaign wasn't the best idea, MP was a resounding success on its own, with four DLC packs that were released for free and gathered a large following. It finally allowed us to explore new gameplay possibilities, test out new powers, new races, and new combinations that were never possible in SP.
So my answer to MP in the next Mass Effect: Yes, Yes and Yes!