Its irritating when you have a bunch of vehicle squads to remember which one you can add a particular vehicle to. Why is there a restriction ? If it has to do with crew level, then allow ANY vehicle from that crew level (and nation) to be available (or less) to that squad.
For example the M4A2 can be used by the 69th tank battalion but not the 32nd armored regiment (it only allows Jumbos) or the 4th tank battalion (which allows a number of US and British vehicles as well as the Grant). Why the limitation ? Is it a remnant of the older system of selecting battles ?
Inventory management is already a nightmare as it is, why make it harder ? 