I know it is sinful to ever mention anything that has to do with the "dark arts", but this is just too cool.

I wonder how this would work for CL? We could use a bell crank and PR going to the back two motors (which would be mounted on a hinged rod) and another PR to the front two (same), or a PR going fore and aft to mechanically operate a TH control for the fore and aft motor speed. The inboard and outboard motors would be hooked to a simple arm (like a combat shut off device) to control line tension via small roll or yaw.

This German (good English subtitles) video is a little long, but interesting. At the end of the video it gives all the system details. I was surprised how similar it was to the stuff we use in our models.

http://mikrokopter.de/ucwiki/VideoAbspielen?id=188

Pro: 

1. We could finally get the "real" sharp corners the book says we should get!
2. We could fly at any speed we want. Great for CL beginners too!
3. We could accurately program the pattern. (With several hundred thousand $s of programing?)

Con: 

1. It might cost a few extra $$$$ more than the average ECL plane?
2. Howard would disapprove within 2 ms. 
3. The judges would NOT accept it as meeting the BOM rule.
4. The judges would NOT give you a very good score, just on principle!
5. Waaaaay outside the box for CL in general.
6. May meet the letter of the rules, but even I think it may not meet the "spirit" of the rules. 

As a side bar: a few years ago I suggested, on this forum, that we use a small motor inside the outside wing with the prop perpendicular to the flight path. This would keep a constant line tension using a combat shutoff type device to vary the speed of the small prop as needed. I think we all had a good laugh at this then, but after seeing this video I think it may work better than I originally thought it would.
 
Those working toward the 2-4 break for ECL may be interested in this?

BTW: Even though some of my good friends fly them, I still dislike Helicopters. They will muck up an RC or CL field if given the smallest opening to do so. But this video is still cool and I appreciate the great technology.