>>1727426>why can't existing bikes be modifiedthey can
It's called an s & s coupling.
Ritchey makes breakaway frames too which is a similar thing.
The thing is, you don't want a poorly engineered version of this for obvious reasons. And cabling complicates how easy it is. It's something that's useful in very niche scenarios, you wouldn't want to be assembling every day as part of a commute. It's not that easy.
