HMan, sympathise with you with your arthritis. I can understand why you are always trying to find easier methods and practical ideas with your inventions but if something out there works efficiently the same way as you had planned, save yourself the trouble and use it, you ain't getting any younger.
I too have arthritic flare ups at times and I have tried to make best use of the most rigid poles, best brushes, angled goosenecks, etc, etc. Have always tried to look after my health the best I possibly can by avoiding all the terrible ideas associated with wfp and trusted what I know works best for me.
It's about compromising on weight, rigidity, ease of use, scrubbing/rinsing effectiveness and using less energy to get efficient results. I use larger diameter hose reel and hose pole with a higher flow of water for cleaning which speeds up my jobs, it just means I don't have to work flat out every day so am able to have more time off nowadays which suits me fine. I stopped doing all the add on jobs years ago and just concentrate on the glass and nothing else. Always pass wet weather jobs on to others as it's too strenuous and prefer not to abuse my body with strenuous work nowadays. Life is too short to bugger your health up and need to respect your own bodies limitations the older you get.
Every now and again I have to manufacture something to suit my needs i.e adapt my own goosenecks for radial light brushes as theirs are too short for commercial work, etc. Changed my methods of cleaning technique to suit my illness.
I use to do a lot of kayaking in my youth along with Judo and Kung Fu. About 5 years ago I took up kayaking again as it's relaxing and good for core muscles and overall strength allowing suppleness. I struggled to begin with trying to find a suitable paddle. Thought about giving it up but perservered and realised a crank paddle with the twist and loop in it was ideal for me after trying several different ones, found it the most comfortable and suited me perfectly. Thus my love for the sport grew once more and every chance I get I'm off down the beach riding the waves with a surf kayak.