I don't think that this would be a good idea.
When I look at my own land and imagine I could upgrade everything remotely, I would capture my whole city and surroundings within a few days. With new players joining the game constantly this would give them very little chance of challenging the "older" players.
Something like that should if realized be very expensive concerning that it is somehow against the games spirit (walking around and explore your surroundings). So, one would only use it for very remote locations he might never get to again.
The only thing I would suggest in this direction would be to be able to choose which land to upgrade within the known 500 meter radius but not only your nearest land thus having farther to move close to your lands to upgrade them.