I can see it being useful on gridded maps as well. If you're moving a considerable distance (riding a horse, dashing, etc) in a zig-zag path, counting squares gets tedious and it is easy to make a mistake. However, I agree that differing movement rates would be an issue. Perhaps allow unlimited movement (as today) if you just left click and move, but if you left click and then right click, cap the movement to the token's maximum move. I still forsee some difficulty, as the latter is part of the sheet, and interpretation of the field probably varies from game to game and map to map. A token of a wagon moving overland on a province-scale hex map is very different from a PC token moving on a 5-foot square-grid dungeon map. And some dungeon maps use 10-foot grids. Still, they could probably find a way to tag a field (or fields) on a sheet in a way that could be queried to get "squares/hexes of movement allowed" and derive the value for that from the visible game-specific setting. Another complication is that token movement can be reduced by encumberance, or spells like slow. And terrain can reduce movement rates (5E "difficult terrain", for example). So the number would still in many cases be more than the rules allow for a character in many situations, absent a lot more features to identify/calculate all of those states. Although I'm throwing out all those negatives, I do think that deriving a maximum movement in squares from the sheet movement would be a good thing. And it could easily be tied to encumberance on sheets that support that. My players often ask me "can I move to here?", and most of them are comfortable with the ruler, and being able to make a first approximation before they ask would be handy, So I'm throwing in my vote.
