smell the smoke?

  anyways, two systems I want  to get, the OP system and hydrotechs proracer for TM (for hardfloors) seem like they could be combined in an ideal way.  The proracer is like a rotary machine that sprays water down and sucks it right back up while agitating with a rotating brush.  All within the self-contained head casing.

   http://www.webnow.com/lib/get_photo.asp?photo=photo&id=10003&unique_=rotovacbest16031035 - http://www.webnow.com/lib/get_photo.asp?photo=photo&id=1 0003&unique_=rotovacbest16031035

  If I am not mistaken, what makes the OP system so effective is the '360 cleaning of each fiber (all the nubs rubbing the carpet in an oscilating motion), and the extremely low amount of moisture/residue left when the job is done.  What makes a truckmount so effective is the heat, the flushing action, and the water pressure. 

the proracer sucks up the water as it goes down. High psi literal flushing, a constant flow of clean water across the fibres as they are agitated by the brush. 

I can picture a proracer type unit with an oscilating head, and instead of a pad, a brush whos head pressure is adjustable to thickness of the carpet.  The cleaning solution would be sprayed down as usual per the OP method, but rather than agitating and removing with oscilating terricloth, the agitation would be performed by an oscilating brush, and the solution flushed out and removed by the constant water flow and vacuum.  There would be a minimum of water left on the carpet and even that would be clean water. 

  From what I've read the factors that add up to clean are, agitation, detergent, flushing action, and heat.  A unit like this would do all of that and leave zero dirty water or residue behind. 

bad idea?

Hold on a jiffy, the Pro Racer is a controlled pressure washer. It does not have a brush on it only spray jets and must have at least a 1000 Psi type pressure washer to operate it, along with a vacuum system that also has an auto pump out system.

These units go through up to 4 gallons of water per minute.  With out a Truck Mount holding tank or Auto dump a small vac system would be down dumping manually more than operating.

Also the Pro Racer has a height problem because of the electric motor it will not go under and into small crevices like under oven's and other electrical appliances etc. etc.

The product of choice for me is the new Turbo Hybrid. No electric motor eliminating one cord and very low profile. Now if you wanted a unit with a brush look at the RX20 from Hydramaster.

It is on this site.  Both these units are for hard surfaces only and not carpet with the exception of the RX20. With the RX20 different attachments can be bought to also do carpet.  Now the closest carpet tool to fit your description would be the Hydramaster Dri Master Rotary.

This unit cleans with ease and leaves carpet very dry very fast.  You also mentioned Roto Vac.  This is a fantastic unit for restoration work, not fast but very thorough on trashed carpet.