From a developer standpoint, the maintenance doesn’t change one bit. What you’re updating is the only thing that changes. If you’re using version control (like any good developer would do), it’s as simple as clicking a button or typing a command to update. Or, it’s as simple as doing nothing if you have an auto-update script running.
Anyway, it’s no more or less “maintenance heavy” than updating a parent theme from the developer perspective.
However, it is less of a burden on end users who’ve made mods to their child theme but want to continue getting the best of the new stuff from the parent theme (note that end users shouldn’t even know that they’re using a “framework”).
Hybrid Core (my framework) isn’t one of the oldest and most-used frameworks for no reason. I’ve taken the actual framework approach for many years and rarely have to worry about common user issues related to this subject.
And, just to be clear, this is not my solution. Carrington and WP Framework were doing it before I was doing it. And, loads of other developers were utilizing frameworks before then.
Additionally, the “solution” doesn’t necessarily have to follow the “framework within the parent theme folder” path. It could just as easily be a plugin. I don’t personally do it that way because I think that puts more burden on the end user.