Actually I want closer to 6v off of two 3.7v batteries for cartomizers. Just because 7.4 makes them burnt. I have no real reason to go to 5v unless I wanted to use stock atties, which I used to do on my V2.
6v carts are perfect for me, I just want to be able to use my Big Storm to vape them

And unfortunately 3.0v battery options are very limited.
as far as the 26650 goes... I was just drooling over that whopping 4000mAh
But there are still many people that prefer 5v...and I think the only reason is that for many its a stepping stone from 3.7v vaping to HV vaping. But there are mods out there for that... the GG doesn't have to be one of them, unless a resistor disc was available to let them try.