I've worked with several excellent people in my career who progressed from customer support to QA to QA engineer to software engineer.

It's not common though, and I don't think it's a case of "training". Some people have the drive to figure that path out, and those people should be encouraged and supported.

> Some people have the drive to figure that path out, and those people should be encouraged and supported

Totally agree. I don’t think that means institutionalizing that pipeline is likely to yield those folks. They’re rare.