Bah, EM's will still be going strong when "modern" pinballs are gathering dust.
Sure, we'll have to improvise a bit more-- maybe the coil you get will need a few dozen turns of wire removed to be the correct strength, or the spring you get will need a little adjusting, but people will be able to cobble together a fix for almost any problem these old machines have long after we're all dead and gone. Can you say that for the modern stuff with their chips and circuit boards and digital displays?
3-D printing will solve a lot of our problems, and backglassess will stop being a problem when printing improves just a little bit more (maybe brand new play fields too!). In fact, in a few years we might be routinely restoring machines that are considered too far gone today.
Maybe the biggest problem we have going forward is the greed of the people who try to limit the production of parts. Just look at what happened to Pinball Rescue-- one letter from an attorney and they stop making all their Williams plastics. If the money guys would just step back and leave us alone I think it's only going to get better as time goes on.