I am bored of the churn associated with stuff higher up the stack. I would prefer to master a craft rather than chase new fads every few years.
Also, you won't be required to work on pet side projects, push them to Github, blog about them and post Show HN comments to build up street cred for future job interviews.
But I have no idea how one breaks into this field. Maybe that's worth an Ask HN or a Stack Exchange post.
I learned enough to know when to call IBM for support, but with that experience it wouldn't be too difficult to find another job managing one.
I remember 12+ years ago, my old boss bitching about working on an AS/400, then he'd hire his brother (who worked on them for years) to come out to do very simple stuff for quite a high premium.
I just wish they weren't so proprietary, but at the same time, I am glad they are. It's been a love hate relationship.
Now I work with an AIX system. Unix under the hood, but IBM still has a stranglehold on it. Both tanks though.