I also like the idea of 2 cells, but I guess the driver’s and Led choice may be tricky to make that possible 
Why do you think it wouldn’t be reasonable to use a triple in the ET1? Due to heat dissipation or internal space? Or any other reason?
I am not familiar with those Nichia Leds, thanks for pointing them to me! I wanted something like a “hot rod” with 2 cells, but I don’t see it coming…
About the VG10, I’m still on the fence to see if I will use a quad or not. I will try to check how a White Flat behaves on that reflector and decide it I will turn it into a quad or not.
Still, about the ring to hold the o-ring, what would you need (measures) if I wanted one? I may get the materials and the try one or other solution depending on how good I can put them together!!