Would like to retrospect to this interesting thread...
As per Honda Japan info, the biggest, seamless tank for 2017 & up is 16 L.
https://www.honda.co.jp/CB1100/spec/
燃料タンク容量(L) 2017 & up CB1100RS-EX=16 L/4.4 gal
But, I heard a lot of rumours about 16.8 L seamless tanks, as well as, I read a few articles, confirming almost 17 L capacity ...??
Local, US or CAN markets may differ.