Ed implied on the livestream that they'll do most of the balancing in the time after release, once people have played with it. I have to image the Dutch would be prime targets to get something, since they do get penalized a bunch right now for building districts on rivers, with nothing to really counteract that. They can't really get immunity from flooding, since Egypt is getting that, but definitely I could see them give Polders something extra, even if they are already very powerful (even just something simple like any tile next to a polder is immune from rising sea levels). Although on the flipside, if they do nothing and the flooding mechanism actually let you build fresh polders on flooded tiles, that would actually help them a lot. They should be praying for rising sea levels to sneak in extra inland polders.