Still seems like a hypothetical problem to me. I know the early machines had high failure rates, but Stern stepped up and provided replacements well beyond the warranties. I had a v2 board go out and it was easy peasy to get a replacement.
I haven't heard many issues with the late version boards, and only vague rumors of a couple people actually paying for replacements.
They will go bad eventually, but I believe aftermarket repair capabilities will catch up by the time it is a widespread problem. How was the reaction in the 70's when the first boards came out, were techs immediately capable of repairs?
At the end of the day, a replacement board is about 5% of the cost of a new machine, so it's not great, but it's not a life changer. I've had 5 spikes and had $0 out of pocket for boards.
I'd love it if stern charged a more reasonable markup, but based on the pinball market these days, that is really unlikely.