While technically true they fit multiple ranges, I don't really consider nanobots to be micro or minibots, even thought they are. In my mind they are separate.
I only mention possible minibot and microbot only categories because setting them up would be relatively easy and painless. We already have all the battles for those robots done, they just need to be arranged differently. This would hopefully stimulate more interest in microbot and minibot development.
As for other rumbles. I think they would need enough interest to really justify a rumble for them. Though a Robot only one is probably a bit overdue.