from what I have read it is the Spike TM system is the same one that was used in The PIN with linux on a particular chip in that board. It then links to 4-5 other small computer boards under the playfield to then control all the functions.
like what Rob said while Stern are going strong there will be spares to keep machines going.
I am more concerned about games that run lcd's like JJP and Heighway, what happens when the lcd dies in a few years time and you can't get that model anymore or if the company closes then all lcd stock will dry up then you will have a game that loses alot of it's features and scoring. I still like my dmd, symbolic of the era.
I like where Fast Pinball is going with having a dedicated circuit board with a socket for a beagle bone black or a plug for a Raspberry PI to cable connect. Then the code and dmd art is stored in the mini computer and runs via python via Mission Pinballs Framework. If you get a game with this unit in it, you can simply buy 1-2 spare beagles or PI's and store in the pinball spare parts box for $50 each.