The Harasser is the best example for crewed MBTs.

A bit too elaborate in my option good man...

With the amount of redesign needed they are basically going to be redoing the MBTs from scratch, and they might as well just make a NEW Vehicle if that's the case...
It's probably going to be a lot easier to swap the Gun Controls on Prowlers and Vanguards (A simple tweak of coding) and change out the Guns themselves on the Magrider (A bit more complicated, as this requires altering Vanu Tanker's inventories and the individual weapon models).
This leaves far less model and coding work to do, which also makes it faster to implement into the Test Server.

I do agree that SOE is unlikely to enact that much change, possibly (probably?) due to the players who've spent real money on their tanks already getting quite miffed when truly drastic changes happen. Giving drivers limited-traverse hull guns which would be less powerful than the main gun would have been a fine compromise from the very beginning in my opinion, but one cannot change the past.

Well then SOE will just have to suck it up and make the game better, regardless of who has paid for stuff.