What is bad with using the wrong cable housing? Thanks to Nate W's answer here, I know that there are different cable housings for brake and shifter cables. Assuming the cables match the housing diameter...

What would happen if I used the spirally-supported housing for a shifter cable?

Maybe answered by Would using compressionless brake housing for derailleur be a problem?


What would happen if I used the lengthwise-supported housing for a brake cable?
spiraled brake housing would compress when shifting which would diminish the accuracy and using lengthwise cables for brakes can't handle the stress and split wherever the tension is too great.
this article explains as much: https://www.pinkbike.com/news/To-The-Point-Shift-Cables-2013.html