Totally feel this. I once found an entire site built with nothing but MySQL timestamp. I switched everything over to DATETIME, but since I did it in a straightforward way, I kept worrying there were hidden bugs lurking. In the end I just closed the laptop and thought, “whatever happens, happens.”

Guessing this is fixable on an incremental basis?

If all new software now starts using 64bit then presumably in 13 years time it's only a long tail of never been updated software that is an actual problem