This is purely and utterly a nonsensical idea. We don't want pinball to be like the automotive industry. I believe it was Mr Ford that said, "we don't make cars to make money, we make cars to make money out of spare parts." or words to that effect.
I believe that all new machines should come with some sort of guarantee that the code, if not already on the machine, will be completed up to a stated level e.g. all features/modes will be operational within a stated period of time. Once this has been fulfilled, then and only then, I MAY be prepared to pay a small amount i.e. well under $50 for a 'special' update that is above and beyond when the stated code is considered as finished.
We have already seen Stern software can be hmmm modified in that we can add our own songs and some other bits and pieces. You seriously don't think that if we have to pay for software updates that the manufacturers system wouldn't be hacked or pirated copies made before a week was over.