Thank you very much Aristos - you've shed light on an important point and understanding the game better through the code is always a plus.
At 20 turns, it's not as bad as it sounded before, but it's still pretty bad compared to a mechanic that simply ensures a player keeps his promise and *actually* moves troops away.
Also, if a 20 turn NAP is created, it should be known to the player how long it is, not hidden.
And yes, holding a key like shift and clicking should create a waypoint. Waypoints are the stuff of 90's games; every turn based strategy made since then should have them, and if something obstructs a unit's movement along a waypoint after it's created, the game should stop the unit and prompt the player for new orders.
That kind of stuff isn't rocket science, but historically civ developers have been absolutely awful with it. The most extreme example I can think of is Warlords II (made 1993 or so) properly interrupting a blocked unit's pathing, while Civ IV BTS (over a decade later) would auto path the unit backwards if the way was blocked, unprompted
. Sometimes it's not a bad idea to keep working concepts from previous games if no better alternative is placed instead
.