Brink will NOT make you pay for micro transactions, you buy the game , that is it, no monthly fees, no buying guns and cloths, etc.
DLC's might be released after the game is released, which would include maps, new archtypes, tattoes, etc. (This is a speculation and they have NOT said what wilk be in future DLC's, if any)
Tho they will not be giving out gun DLC's because that would unbalance the game and cause more trouble then it's worth.
Really if you think about it, Micro Transaction could be better.
Well think about it, You buy what you want, Only want 1 Pair of shoes for $1 instead of paying 10 for a whole bundle( Like most DLCs are) of other things you wouldn't want Save 9$ right there.
Now that wouldn't work for maps per say. But I guess when you water it down it's all Pros and Cons.
( I know this game won't do that though. I'm 95% sure, It' just isn't economical for companies )