Unless you break or wear out a shifter, I don't think there's much to be gained in converting this bike to 11-speed. It seems it does everything you need it to do, 9-speed parts will continue to be available, and any new bike you get in the future will likely have an 11 or 12 speed group on it.

edit:

Not to mention, you have your own special subforum: https://www.bikeforums.net/early-bri...s-7-8-9-speed/