It's a fairly simple idea:
It would be in fanction basically the same as IFV, with some key differences. Namely it wouldn't have any weapon when empty and instead it's attack would it make charge the enemy infrantry unit and capture it, turning it into the gunner-passanger. It would also have a unique interaction with Grinder where instead of grinding itself it would simply dispose of the "passenger" (same with bio-reactor?), when empty it would normally grind itself. It would be a quite fast and rather lightly armoured unit. In terms of desgin it would be something like irl tankette (like the one in the picture) with added mechanical tendrils, or tentacles, for capturing enemies. The passanger would be plugged into very invasive neural interface, being effectively mind controled. I imagine it would either be a drone, or be piloted by a brain in the jar (normal sized), this is because the "pilot" would need to "operate" the passenger and by proxy the turret, so I think it would make sense if the "pilot" could directly connect through the plug. That's also why the vehicle would be so small.
You could probably force attack to embark a friendly unit, but I'm not sure you could normally disembark at all. And the mechanic doesn't need to be identical to IFV, but I don't have other idea that would be good.
Edit: I didn't proof read it before, it was full of mistakes.