For substantial runtime improvement, i think 4x or 8x 21700 cells (the LG 4800mAH in particular) would be more advantageous without the large size/weight penalty of 26650s...

Or 3x / 6x 21700s to be more size interchangeable...

But there's the cost of custom machined tubes/carriers or somehow lobbying manufacturers to adopt more capacity in their designs, with interchangeability between models a big plus to keep costs reasonable.

IIRC Acebeam had some battery tube "Lego" options before.

I use my monster lights quite frequently and fumbling with more than 4 cells at a time gets a bit tedious. A better spring-bypassed mousetrap is in order.