I completely disagree Younes. The issue is because the player base is split across multiple beta versions right now - I haven't touched MP recently not because I don't want to but because as I'm in 1.4.1 I can't play on the 1.4.0 servers.
That's not a good point. We had a lot more players some weeks ago, even with multiple branchs already there. MP is just dying because the combat is bad, the class system is bad and servers are trash. Just playing MP is enough to see it. Every time you join a siege, there are some people already saying "hey guys, you ready to crash ?", "crash in 3,2,1...", etc. The bad shape of MP is on its way to become a meme.
edit : but it stays dumb to divide the MP across multiple branches, i'll give you that, it's just not the main reason MP is empty.