There aren't that many people making a career of it today, all things considered. Are there even more than 1000 people in the world making a living in this industry (production, sales/distribution and operators)? It's a niche industry at this point and may stay that way indefinitely. I think we'll see more one-off type games being designed by hobbyists, maybe more small-run boutique type stuff, and products such as P-ROC that lead to that end. Maybe careers for younger designers will come out of the custom-made stuff and maybe they'll get brought into the Sterns and JJPs of tomorrow.
While there's certainly less chance for public exposure to pinball at this point, something that's different is that games are probably less likely to be destroyed when coming off of routes or when people get tired of owning them. That means more games in people's homes. Really if collectors hold onto them and pass them off to other collectors, there's no reason the current NIBs wouldn't be around many years from now probably in roughly the same volume. The issue would be whether or not replacement parts are available to keep them up and running indefinitely.
There are quite a few expos around now, too, and I think kids end up going to those and liking them. I think the expo craze is pretty recent. My local Louisville Arcade Expo will have its 5th annual event this year.
I find young kids of my family and friends interested in the pins when they see them at my house. If the generation of late 20's/early 30's who are just now at the point where they can afford pins end up passing the interest onto their kids, there's a good chance people will be interested for a good while yet. I sure hope when I have a kid that I am able to get him or her interested.
I think what pinball has going against it is that the current late 20's/early 30's people are among the last to have memories of abundant public arcades. I think a lot of what drives the desire to own games is the nostalgia factor, well and that it's just awesome! I fall into this group, but admittedly wasn't into pinball as much as arcade games as a kid, so there's hope for others to get into pinball later in life, too.