Thanks @jeremiah.foster . I had not configured Exim to run, so I've followed your instructions here to disable it. But back on topic, I think my boot time already was fast, before I upgraded my kernel and ran into this issue where it just hangs forever while trying to boot. Disabling Exim definitely didn't fix that.

Hi Jeremiah, I understand the difficulty, and would love to provide as much detail as I can. I've attached the output of that command, though (spoiler alert) I don't think it's terribly helpful:

After recently upgrading my kernel I had a very similar issue. You basically roll the dice to see if the new kernel will actually boot. Sometimes it will. More often it won't; it will just hang forever with a message much like this one: