Make it trigger under certain circumstances but then make it trigger 100% of the time...
Actually, after thinking about this a little bit longer, I don't like this idea so much. The abandon mechanic is fun to me *because* it happens out of nowhere and it's not predictable.
When it happens it's like everyone collectively is working to stop it/ repair because they weren't prepared for it.
I've had the most fun when I've got to drop an offensive just to try to coordinate with my teammates to set up security while we repair the tank.
I have maybe some other ideas about it to make it more of a minigame or something that is less punishing for dives.
1.) One faction should not be better at recovering abandoned vehicles any more than the other (USF crit repair lol) for fairness reasons.
2.) Troops cannot get inside until it's fully repaired and there can only be so many engineers working on the tank at one time. The idea being that there's a consistent time for repairing the tank and if someone dives into enemy territory they aren't f*cked just because there are a shitton of engineers there. Also it can lead to battles around the tank to retake it and the enemy can't just hop inside to deny the enemy a chance to retake.
EDIT: Also, it would mean that you now have options to halt the repairs or slow them down, as you could shoot the tank to get the health down with AT guns or another tank and force the enemy to attack or else not be able to recover the tank.
EDIT2: Though maybe this would be kind of a snowball with the more numerically superior team being able to force the weaker team off the team and lead to snowballing. But then again it would make it a risk/reward choice, either you risk putting time into repairing the tank (possibly putting yourself into a bad situation if they can push you off it and take over the repairs) and be rewarded with a cheap tank OR you take the safe option and finish off the tank.
I think it could make abandons more of an interesting mechanic and less of a bullshit RNG roll that fucks someone over for bad luck.