I feel like it would be fun if fully functional tanks where added to the game either by the devs or as a mod. For example an M4 Sherman or a Tiger 1. I think people would enjoy that.
They are a small pain in the butt to jbeam, there were a couple proofs of concept (tracked vehicles). For now you can play around with this: https://www.beamng.com/threads/simple-tank.51425/ As for a Sherman or a Tiger 1, some modder would have to be willing to make that, it won't happen otherwise.
There is a Tank from modsgaming I wouldn't recommend downloading it, as it probably doesn't work, and I have gotten sketchy ads from downloading from this site before. I'll give a link for reference. https://modsgaming.ru/load/beamng_drive/mashiny/mod_tank_t_80ud_dlja_beamng_drive/38-1-0-18359
Thats true, i thought about that a few minutes after i posted this. Still, i wouldnt be surprised if one day someone decided to put the time and effort into making a fully functional model.