The recent post, It should be called the Mibo Transformer, showed the quick-folding Mibo “Faltroller,” which had some intriguing folding handlebars.
A quick internet search turned up two aftermarket folding handlebars for bicycles, one still just a concept (and apparently a prototype), and one ready to buy. Both seemed to be aimed at people keeping bicycles in narrow hallways, and while they will help, a bike still has pedals, which can’t be easily folded.
But a full-sized footbike with these would be only as wide as the folded bars. They would also facilitate easy strapping of a full-sized footbike flat onto any auto roofrack. Worth $152? That’s up to you.