> Some people may not heed the notices and their systems will crash
Some of these systems are indirectly responsible for keeping people safe and alive. This "oh well, you should have paid attention and taken care of it" attitude won't fly.
Seriously, this is something that could have been rolled out over the course of years. They could have talked about it at industry conventions and otherwise socialized the idea of updating dependent systems. Are those mission critical systems just willy-nilly connecting to these systems? Or is there some authentication? Because if there's authentication, there's usually some record of contacting the admin of that other system. Like how API service providers know who the owners of API keys are. Make it a required step of their annual FAA filings to certify that they have become 5 digit compliant (or whatever it gets called). If there's a way to make them prove it, make them prove it. If it has to be done to each aircraft, require it.
You get my point, there's so many practical ways to handle this. That's not to say it's easy but it's possible. Even just an audit of systems relying on communications to these legacy system(s) for actual flight operation would be a useful thing that I'd think most airline operators should have documented somewhere.
My thought in that comment was the further way from mission critical systems are the ones that will be more likely to unintentionally ignore the switch over notices and have a crash. At that point we're talking about Kayak.com going down or something that is absolutely not mission critical.
We need to have a way of rationally solving this issue that's not just some throw our hands up and ignore the problem until it's critical type situation. It a reality of our technical world that old stuff will require some breaking updates at some times.
Some of these systems are indirectly responsible for keeping people safe and alive. This "oh well, you should have paid attention and taken care of it" attitude won't fly.