Really, really cool idea, but assuming I understand your intent behind this proposal, you might want to add the following:
- A unit that is inside a transport may not be targetted by any commands or enchantments (units outside a transport probably shouldn't be able to attack/enchant units inside it)
- A unit that is inside a transport moves along with that transport until the unit is unloaded from the transport (right now there is nothing specifying this, so a unit inside a transport would remain on its original square and then "teleport" when unloaded)
- A unit may not be inside more than one transport at a time (I don't even want to think about what would happen otherwise)