diy or kit cargo bike extensions

http://www.instructables.com/id/Xtends-Convert-Your-Bike-Into-A-Long-Cargo-Bike/

This is a welded kit.
Chop up 2 bikes carefully and you might manage a front boom/ SWB bike.

http://www.instructables.com/id/Cargo-Rack-Bike-Sport-Hauler/

Bikes that Haul People

In East Africa, there is a population of small business entrepreneurs known as "Boda Boda" operators who use bicycles as taxis. Most start their business by purchasing a standard bike and retrofitting it with a locally manufactured seat post and special seat cushion to accommodate passengers in

back.http://bikefriendlynorthshore.wordpress.com/2010/05/05/longtail-cargo-bikes/

D: I saw an extracycle in town. A mother was shopping with it. She said she can put 2 kids on it.

Why I was thinking of it?
I just went to great effort to reattach a bike rack to my Cruzbike kit.
The Mongoose chassis is a cheap supercycle.
The frame geometry is unusual, being rectangular.

I use the 'assit mount' to carry all the weight.
The aluminum part sheared, so I had custom steel replacements made.
Which never quite lined up.
So much tapping and drilling later, it is finally on again.
... standard frame geometry is a MUST for accessories!

I see recumbent bikes in town, and their frames never allow standard upgright bike accessories to be attached. Why reinvent the wheel?
I was thinking about this when I saw the cargo bike extension.
Is there any reason a 'bent bike could not also take a cargo bike extension at the rear?
This would allow me to have a long-wheel-base SWB for touring, with cargo capacity.
But then- take it off- a standard wheelbase SWB short wheel base.
Obviously, this makes the design tricky. It could still be a Flevo Greenmachine knockoff, sans frame suspension.
(A thudbuster, though not cheap, is still far cheaper. Assuming it works.)

I am also considering having some internal storage in the bike frame. Just use pressed sheet metal or plastic to enclose the chain area, with mount points.

The detachable-externa-frame-rucksack-seat-back is enouraging a fat-ass-granny bike seat on the bottom portion. I saw some ridiculously oversized ones at McPhails.
I don't see the point of a seat bigger than my ass, though.

Hmm, variable steering -at least maybe a swap-out cog for long/short wheelbase mode- would duplicate car 'power steering' in some respects.

I continue to ponder the left /right weight symmetry and how to get various structural elements to add up correctly, including both top and bottom chains.