I think I have a working solution for the chokepoint/bottleneck problem described above:
1. Movers between neighbouring areas are allowed to stack with other movers of all kinds on area departure and arrival waypoints directly on map border (crossover waypoints). This is an exception to the one mover per square rule.
2. To minimize potential mutliple movers on one square situations, they will immeditaley leave such crossover waypoints on area border, overriding any departure time settings.
3. All of this is only true for time driven movers on crossover waypoints between areas (on each side of area border). All other situations still adhere to the one mover per square rule. Arrival locations for movers teleporting/spawning into an area without smooth transition will respect the one mover per square rule - in occupied arrival square cases the code tries to find a fitting alternative nearby arrival location. Movers targeted toward a non-neighbouring area will also not enter an occupied departure waypoint square - instead they will simply teleport from where they are towards the non-neighbouring area when the time has come. Both behaviours - teleport in arrival and teleport off departure - are flagged with "Just arrived here" and "Heading off" floating messages respectively.
First playtesting of this looks very promising

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