I'd love to see an example of a project that has been actively developed for 20 years and has made a similar change. Linux comes to mind as a project old enough that has been kept updated regularly, but it has always been good-old C (not sure, though, maybe there has been some changes introduced)
(I'm not trying to be sarcastic, I think it will be interesting to see how they faced that kind of change)
You're right, migration may be needed at some point. But "at some point" is a very fuzzy definition, and my guess it that it will be later rather than sooner, giving the complexity of it. Paying interests of technical debt for this year, and we'll talk again next year indefinitely may well be an option if getting rid of technical debt is too costly. Sure, you'll pay more on the long term, but each year you'll face the same question: "Should I do this costly long term solution, or just keep going whit relative pain for a while?"
You're right, migration may be needed at some point. But "at some point" is a very fuzzy definition, and my guess it that it will be later rather than sooner, giving the complexity of it. Paying interests of technical debt for this year, and we'll talk again next year indefinitely may well be an option if getting rid of technical debt is too costly. Sure, you'll pay more on the long term, but each year you'll face the same question: "Should I do this costly long term solution, or just keep going whit relative pain for a while?"
I loved this tweet today by Brandon Rhodes about this: https://twitter.com/brandon_rhodes/status/421309568158019584