You actually can get Tanks as battle support already in some missions. It will appear in the mission description.
In terms of adding them to your Lance as something you can control directly? Not at the moment.

thanks for the reply.

i've never noticed this so i'll keep an eye out for it.

I have them as selectable units in the mechcommander mod. Never did refresh their AI, so they kind of suck at following orders. Definitely possible to spawn them as support one way or another, just not sure how you'd command them in normal FPS mode.

Someone could do a whole salvage system for them, but that's a pretty big mod to add in the other supporting UI, etc.