I first proposed an idea similar to this ages ago.Mine was more geared toward the then talked about Commander role,where one person on the team was essentially the field general stationed in the MCC and what ever WP was earn was used to deploy turrets,extra CRUs,Orbitals,and my idea,extra vehicles.Since the rumor o the Commander never came to fruition,none of this really works now,but something absolutely has to be done about tank spam.

I think the OP's suggestion is way to restrictive and just wouldn't work,but there is a much easier solution.

1)No SP free tanks,or any vehicles for that matter.This one simple thing has completely destroyed the balance of vehicle vs AV warfare.

2)Due to the fact that it's still 16 vs 16 matches,there's absolutely no reason in any game mode for there to be more than two tanks on the field per side at any given time.I couldn't care less if you feel entitled just because you skilled into them.The facts are that they have completely broken the game,and people don't play broken games for very long,so for now and for the sake of the playerbase,there needs to be stronger limits.

3)There needs to be a severe cooldown period for people calling in vehicles,taking massive damage then running away to recall them,only to call them in two seconds later.Whatever vehicle you recall,you should restricted from calling in that class of vehicle again for a minimum of 5 minute.If it gets blown up,that's a different story,and if you call in a DS,recall,then call and HAV,that's ok too,but think of it kind of like the rule in football where you can't call two timeouts back to back.