Can't dismantle a 18650.
Other battery 14650, same length but 2mm less wide, capacity wise they have less, about the same as scud, so again, only gain here will be with 2x18650 or a design that will accommodate 3x Scud's, but problem with the 3x Scud is price and availability.

2x 18650 can be bought for less then 10$, of course here im talking about 2000-2500mAh (pr battery), but even the 2x 3000mAh cells will often run less $ then 2x Scud's, witch also only carry 2x 1500mAh.

So if price is the point to consider then the 18650 are the way to go.

Other features here are to make a Direct port to the battery's like i have when i charge mine, and use power from my N900 to drive small AMP's and such, but having 6000mAh and something like 3C discharge gives you the ability to attach a DIY POWER Led array, we are talking about 60W output here, you can even run a laptop for a while from the N900 then (with a power converter -DC-DC).

So not only power/runtime gains, also a device that can have SERIOUS attachments.