I heard campaign movement speed is disputable ever since Rome 1.
Boosting campaign movement speed in friendly territory (owned regions, regions of factions those agreed military access, and Controlled see area) for army, navy, and agent can be a good adding to Magnar Mechanics.
I think it is better for both convenience and realism
(of course it should be very different moving across friendly territory vs hostile territory).
Plus, combining with already existing Slower Campaign Movement mods will be very interesting option