It’ll probably happen in the next few years. Compiling for PowerPC went away after macOS dropped it, and it was the same story for i386. Running and targeting x86_64 will soon be a distant memory.
That being said, if you have a Mac/Hackintosh/VM with an older Xcode, keep it! You can still compile with the old version, compile with the new version, and stick the results together with the lipo command. I wrote a simple C CLI app and I can put five architectures in one binary if I want (ppc, ppc64, i386, x86_64, arm64) and it’ll run on any macOS/Mac OS X version ever made.
I would love to do something like this, but what happens if I don’t have kids? What happens if I one of them develop a IT background? Perhaps I could curate some pictures, videos, and documents that I feel are important (and not too sensitive) and send it to the Internet Archive so that extended family could always get it. Self-hosting is great until there is no more self.