Besides having a stoker position a young child can fit, like the Co-Motion Periscopes,
- fold like a Bike Friday tandem
- put the stoker in front, with a good q-factor, like Dutch tandems or the Kidz tandem
- Hase PinoDa Vinci and let a kid freewheel like Da Vinci's superlative 'Independent Drive'
but the stock Da Vinci Grand Junction is only $3K)
Cyclemorph (Xtracycle - build this!)
I will not get everything I want, at a price I want. Here's the prioritised list of what I need in the bike:
1. ideal price point is $2K new, but up to $3K works - no Hase Pino
2. pilot position fits a 6' man
3. the q-factor for both stoker and me is not wide - no stoker triple, or crank shorteners
What I want in the bike:
4. the stoker position will fit from 4' to 5'6" without a 'kid back' kit - has a low rear top-tube, and shorter cranks
5. transportable - takes apart to standard bicycle length or better*
6. stoker front - for their view and my supervision
7. stoker can freewheel - because I don't
8. disk brakes - with large rotors that stay cooler
9. auxiliary cantilever rim-bakes (may require V-brake plates) with bar-top levers - for safer descents**
10. a slower cadence for the stoker, as mine is high, achieved by chainring switch-ups
What I don't want in the bike:
10. pilot recumbent - never be that old, and none are affordable
11. stoker steering - only the Hase Pino has it, but I cannot afford it
By price, only a new Bike Friday, Kidz Tandem, Co-motion or Da Vinci Grand Junction are contenders; a used tandem, or Cyclemorph, are contenders, too. The Co-motion or Da Vinci Grand Junction, used or new, could be improved with a $500 S&S Coupler upgrade*: the Bike Friday and Kidz Tandem with better brakes. Here's hoping there's a better solution than a trailer-bike in three years...
* Many tandems have six S&S Couplers to take apart quite small. I think one pair of couplers, top and bottom tube in the centre of the bike, will be sufficient to make the bike much less cumbersome, at 1/3 the cost.
**Problem Solvers Cable Doublers would allow me to minimize levers and brake overheating and maximize stopping. I'd attach front and rear disks to the left lever, and front and rear rims to the right (many 'mini-V' brakes are compatible with STI levers). On a bad descent I could simply alternate the hand I squeeze for a constant speed and not overheat the brakes; or squeeze both in duress.
Addendum: November 12, 2012
I forgot the Circe Helios, for $2000+.
And the Circe Morpheus, for $3000+. These address some of the concerns above well.