That is how I see the limited job system. Thank you for describing it better than I ever could. I don't think the idea of jobs as content is inherently bad. It comes down to execution.
When I look at niche jobs like PUP, BST, BLU, Orator, Mime, Arithmetician and so many others, you get the impression that these jobs would never even be considered of being added to XIV without this concept. And I know that people get attached to BLU thanks in large parts to XI, Tactics, etc, but I think that having it in whatever form (and as much requested side content to boot) is better than people constantly requesting it after every expansion and the devs going, "We're thinking about it."
I haven't really thought about the balancing and cost issues down the line, but it could very well be how things will eventually go. That makes the idea of limited jobs that much more interesting, since it's not a tool do the content like the standard jobs, but rather more like content in of itself. If they can develop and expand the system slowly like they with other side content such as the Gold Saucer, I think we'll have a very reliable and consistent form of side content in these jobs. At least, that's what I'm hoping.