@ Kyle, one of the factions design is crews repairing tanks. Imagine this.
You are pop capped have a damaged tank and a squad that is not full. You pop out your tank crew, suddenly there is enough pop for your queued squad to reinforce the last members. And voila, your tank is dead in the water. Ofc you can use CEs to repair tanks, but taking design into question the solution you propose insnt really all that easy to be honest.
Also, all other factions can go above 100 pop if they chose to steal abandoned tanks as well (and crew weapons for that matter). Not saying it is not exploitable, but it is a complex thing to adress. IF it needs to be addressed.
It's easy then, the solution will be to let you capture vehicles with 100 pop but not with 101.
In your example:
you decrew your tank and your queued squads start reinforcing and "voilà" your pop is 100 now (It won't be higher than 100 because reinforce/production system don't let you overpass 100).. You CAN crew back your tank.
With that solution, nobody will be affected by production/reinforcing queues, you will be able to crew/decrew your existing vehicles but now getting new ones. The max pop you can get with that system is 114 which is only 1 extra tank in terms of pop.
Change your mind, find a solution in every problem.
About the implementation of that solution it should be easy in terms of programming, just make a check before every action of crewing tanks (just as its made for building mines or building units when you don't have the resources or the free cap)
As far as I know, I can start building a tank when my cap is 99, my resources are spent but the tank will never come to the battlefield until the cap is free. This is because the game is checking the availability of pop cap.