good idea, Arthegor !
we've had something like that a year ago, callled "offensive convoys" - you could call them only on an enemy objective (not neutral or friendly), it cost a lot
the game turned into a stupid convoy spamming, that's all ... reducing the importance of helicopters
but your idea sounds better to me. and I'd add - those convoys wouldn't be able to capture objectives, just neutralize them. and it's obvious they should cost a lot
moreover, the units in the convoy are the same units from the objective - so if you send them out to fight to the next one, your objective loses units