This is something many other open world games have done, and I feel it would fit well in Wildlands. I am not sure if the devs have something like this in the works for future content, but nowhere have I found a dev talking about this and there is no indication from the beta this is possible.
You should be able to grab vehicles from hostile factions in the game and bring them to safe houses for later use. I don't really think you can claim you can play the game however you want if there is no ability to save vehicles. Say you want a specific vehicle that is very hard to get for a mission, as it stands now you need to go find the vehicle in the world and fight to get it, then bring it to the mission, and I'm not sure if every mission is going to allow that. It would be nice to acquire the vehicle ahead of time and deploy it when you need it.
I think Metal Gear Solid V did it best, where you only can use vehicles you gather in the field, once they are destroyed they are gone for good. They even went a step further and allowed players to customize them, which in this game would only enhance the experience.
Since the game has a resource system in place, you can balance this out by costing fuel resources to store/repair/deploy vehicles and scale it based on vehicle type. That way a player has to work in order to deploy nothing but tanks and gunships. You should also not be able to deploy them wherever, you can only call them in at rally points/safe houses. This way the rebel vehicle drops still have good use in the game.
TL|DR Ghost Recon lacks the ability to store specific vehicles that players could use to a specific playstyle/need. The ability to store a vehicle for later for a fuel cost as opposed to taking a vehicle in the world for free would be a good trade off. Quality of life features such as vehicle customization would only enhance the experience.