I don't follow your logic - my suggestion wouldn't be any less compact than the SC32, SC52 or SC62.
No extension tubes, just tubes.
I'm responding to the original post (2xAA extension tube) and in particular to the ungainly looking 2xAA Zebralight image. I don't see longer lights being in the traditional Zebralight "smaller is better" realm.
Your idea makes more sense to me personally because it matches what many of us do... instead of opting for longer 2xAA lights, many of us opt for slightly thicker in diameter 3.7V lithium ion powered lights.
For the ultimate in adaptability it'd be neat to see ZL consider an ambidextrous (power-wise) "lego" light series provided a) Zebralight's well regarded regulation isn't compromised by being all things to all voltages and b) one is happy with the diameter trade off (sizing for 18mm cells penalizes those who like smaller AA lights).
On the other hand... I don't need to wait for this. With SureFire + Malkoff (and some Nailbender and other P60 light modules) lego I have the sort of power flexibility envisioned. For the most part I run those lights on lithium ion rechargeables but it's nice to know in an extended emergency I can dig into my huge box of charged Eneloops too.