I don't know if I need the ice to make my character slide longer or have fog make it more difficult to spot enemies or use it as cover as I hack an objective, but I like the idea of it very much.
I think Brink is beautiful and colorful and would benefit from some weather changes.
However, I have such problems with loading as is (i.e. surfaces never loading on time, complete railings missing from some maps, the H.E. charge still in my hands after I plant it) I don't think that the weather effects would be a feasible idea.