I've noticed that I haven't seen an example of two rivers merging together either in the beta or any screenshot. I really hope this isn't a design decision. I know it complicates asset creation a little bit but it's necessary in generating believable rivers.
The possibility of lakes above sea level that rivers can flow into and out of would be very nice, even better than Civ4, but I'm not counting on it. Rivers do have to merge though.
