The broad issue with regard to collecting expensive, heavy and large things is not just acquisition price -- it's also the space requirement and immobility of the collection.
Gen-X/Y/Zers are burdened on an increasing basis with massive debt from college, which knocks them down materially in terms of being able to buy real property with enough space to house same. This also makes them far more likely to need to remain mobile in their living arrangements so they can take advantage of economic opportunity, which means leasing and smaller living spaces -- neither of which is conducive to large and immobile collections of anything. I had the money to collect pinball machines *long* before I had either the space or stability of location -- and you need all three to be a viable collector.
The existing pair of manufacturers have shifted their pricing model to a degree that routing new machines is no longer an economically-defensible act. While there are exceptions in terms of machines that can "earn out" they're few and far between, which means that the secondary and/or collectors market are all that keeps any sort of retail presence for pinball alive.
I don't believe pinball will collapse within the next 10 years, but the bubble that exists now in regard to "value" of these machines is very likely to pop, and when it does it will have a tremendous "flooding" impact on the secondary market. There will be plenty of holdouts when it comes, but come it will, as with all bubbles. Odds are this takes the current manufacturers out as well simply because they have failed to innovate when it comes to the means to improve the cost structure of what they build (so-called "modern" machines are flat-out fails in this regard; I could take half the assembly cost out of a modern pinball quite easily, which frankly astonishes me.)
Those who collect because they like to play won't care much, but those who collect with a glint in their eye of "price appreciation" are going to find half of their so-called "investment", or more, go up in smoke.
Of course this simply means that those of us who sat out the ramp in price, and who collect because we like to play, will add to our collections while those who were playing the bubble game will be crying in their beer.