I don't necessarily read <G21> as prohibiting a host bot nor a minibot from breaking an imaginary plane at the height of deployment line as long as the hostbot nor the minibot is in contact with the pole.
Clearly, a host bot in contact with the pole above the deployment line, or a minibot in contact with the pole above the deployment line before the minibot has separated from the hostbot, are violations of one or more of:
<G20> ROBOTS/HOSTBOTS may not contact their own TOWERS above the DEPLOYMENT LINE. Violation: PENALTY for contact.
<G21> HOSTBOTS may DEPLOY MINIBOTS only onto their ALLIANCE‟S TOWERS and entirely below the DEPLOYMENT LINE. Violation: RED CARD. TOWER is disabled if MINIBOT is DEPLOYED above the DEPLOYMENT LINE.
<G22> HOSTBOTS may not contact their ALLIANCE‟S MINIBOT while any part of it is above the DEPLOYMENT LINE. Violation: TOWER is disabled
Chris Fultz interpretation "The minibot cannot be above the plane of the 18" line after it breaks the plane of the base of the tower." is just one potential interpretation of the rules.
I would suggest Bruceb pose question to the GDC. BUT...
Correction (thanks Vikesrock): the GDC already ruled...and the vertically swinging minibot deployment in which the minbot breaks the deployment line imaginary cylinder is a violation.
http://forums.usfirst.org/member.php?u=33258
I think the deployment shown in the video meets the intended spirit of the rule and the field judges will have enough of a problem with monitoring for violation of <G21> when a pole contact is being made. I doubt most field judges would want to trust themselves to measure an imaginary cylinder at exactly 18". Will we see a special measuring tool?