I'm mindful this is a big request, so if ever, I don't expect it any time soon; if it's even at all possible.
Currently to send vehicles we open the mission and tick vehicles, before clicking dispatch.
I would like to see an ability to dispatch through the map itself, dragging and dropping. Perhaps holding CTRL and then dragging a vehicle onto the mission icon would assign it - this would be useful for vehicles nearby, or diverting a vehicle without having to open the window etc.
Another implementation I would like to see is to type in a vehicle's name into a search box and that sends it when you hit enter or something.
These are all real ways of dispatching. Map dispatching is a brilliant feature that would be a fantastic implementation into MC.