I'll play advocate. Build it and let us see it before you attempt to ride. "Can't" never did nothing and "won't" never will. I've had a lot of ideas over the years. Some good, most bad.
Back about 20 years ago I had the idea of welding two bicycle brake handles together to mount on a control stick in an ultralight aircraft so I could have differential braking. Three friends poo-poo'd the idea because it's crappy aluminum and they said it couldn't be welded and hold; couldn't route the cables without jeopardizing control of the plane; blah, blah, blah. It held for several years and did an oustanding job. Now, I would have never marketed it as manufactured. I would have had it machined from one piece. But it worked very well for me.
Somebody, somewhere built a prototype for the flex bars that are being sold today.