If you are going AFK in a location where a vehicle can reach you, then a soldier/sniper can reach you as well. Meaning you chose a poor place to go AFK.
Inside a building a vehicle cannot kill you and is a suitable "AFK" location for a minute but if you are killed, then thats a minor problem stemming from you AFK-ing.
As for ramming damage, I don't think that will be that good. Mammoth tanks (being the biggest vehicle) would decimate tanks in a full blockade, and realistically, I don't feel this would add much to the game.