I wonder how the market for that is now, and how it will be a decade from now. I imagine a lot of the people with significant experience working with COBOL and mainframes are getting older and retiring
We hired a lot of people from the insurance companies and they all basically said that they would hire anyone with a science type degree that was willing to learn COBOL.
As another user said, allowing people to spin up z/OS would be awesome. As of now, it's not really practical to learn without direct access to mainframes. So all the cost is on the business to train devs. Which is not as important in other dev positions