Re: On what merit will they be trying to convice the users ?
How about simply being able to buy a phone and reload it with an entirely open-source ecosystem?
Don't really give a toss about the open source bit but already done this with Cyanogenmod, 'cos I hate the crap that comes on a Samsung, too. I have lots of Google apps on it because Google works very hard to make them good but, for example, I've never used GMail and use OSMAnd for maps.
The manufacturers don't really care: they'd rather sell you a new phone than provide you with updates. But the market for "anything just as long as it's open source" is pretty damn small.