How about an MRV type vehicle that repairs other vehicles and maybe buildings for each faction, make it limited and expensive to build.
Next could be an ambulance vehicle that needs to deploy and has a healing radius for infantry
Then there could be a vehicle for the commander, I'm thinking the mobile headquarters from tiberian dawn and it would give special buffs in a radius, to nearby units, maybe utilize advanced spotting/radar to make its targets more vulnerable to damage like the guardian tank laser from ra3.
Could even make a new game mode, no bases, just modified crates or terminal on the command vehicle, and the objective is to destroy the other team's mobile headquarters