I have not seen what the new Dashboards look like. Yes, those C# customizations will not transfer over. Sorry. There’s been several discussions on the list (like this one: Planning for the Browser-based world, Kinetic - ERP 10) as a warning to others about putting too much effort into C# customizations.
It’s a good time to distill requirements again to make sure you have what the users need (outcomes - not specific solutions) and see how to translate that into the new world.