It is one of the most requested features by the community, I would bet that they have worked to implement it in the next version. Also, with the increased distance of the routes the weather change would feel much more natural. I'm really looking forward to the reveals!
I'm sure I remember it being said that the sim could already do dynamic weather as it was used in a couple of scenarios? But yeah, it being in service mode would be great.
I think the difference is that the changeable weather in the old version was pre-set (so start sunny, become rainy at x time and then sunny again at y time) whereas the new system is "dynamic" in that it's changeable and more randomised (still to be confirmed) This would however make the 4up challenges more difficult as some people could get rain (and low adhesion) where others don't. Will be interesting to see if dynamic weather really is "dynamic"