I don't think anyone really knows. The vehicles haven't been around long enough to understand what long term maintenance looks like regarding any aspect of the vehicle.

People throw numbers around regarding cost for things like replacement motors and battery packs but as far as I can tell nobody knows how much that stuff actually costs either except the manufacturers, because the replacements so far have been done under warranty. That may not be true for all current-gen EVs though; I've mostly been paying attention to the Tesla stuff.