Bike-in-a-Kit Concept
Yes they have travel bicycles that can be broken down

They typically use S&amp;S couplers
But compared to the time to break and assemble a rack is less tedious.  

You also have folding bicycles
But the don't perform as well a regular bicycle

A break down bicycle is going to have better performance but takes longer for break down and assemble   

Break down and folding bicycles are more expensive  

On a regular frame you are not going to get much benefit from a full disassemble compared to just removing the wheels.  Beyond that lower the seat and maybe spin the bars 90 degrees or remove it.  A full disassemble and  assemble is hours of work and something I would want to do in a shop with a full set of tools.