What happens when you have a high-uptime system where you repeatedly "apt dist-upgrade" and end up installing packages for kernels N+1, N+2, N+3, etc., all without rebooting into any of them?
I agree that if the user manually runs an apt [dist-]upgrade—or really any manual apt command—that that's a good time to do apt maintenance work. (Homebrew does maintenance work whenever you invoke it and there haven't been any complaints so far.) But kernels usually get installed automatically, so it can't just run then.
Now, if there was a specific concept of a "last-known good kernel" (imagine, say, the grub package generating+installing a virtual package when you run grub-install, that depends on whatever kernel you specified as your recovery kernel, ensuring it remains around), then your approach could work—you'd always have two kernels, the LKG for a recovery boot, and the newest for a regular boot.
I agree that if the user manually runs an apt [dist-]upgrade—or really any manual apt command—that that's a good time to do apt maintenance work. (Homebrew does maintenance work whenever you invoke it and there haven't been any complaints so far.) But kernels usually get installed automatically, so it can't just run then.
Now, if there was a specific concept of a "last-known good kernel" (imagine, say, the grub package generating+installing a virtual package when you run grub-install, that depends on whatever kernel you specified as your recovery kernel, ensuring it remains around), then your approach could work—you'd always have two kernels, the LKG for a recovery boot, and the newest for a regular boot.