I do not want to store plaintext logs and use ancient workarounds like logrotate. journald itself has the built-in ability to receive logs from remote hosts (journald remote & gateway) and search them using --merge.
As mentioned in the article, my original use case was: having a fleet of hosts, each printing pretty sizeable amount of logs, e.g. having more than 1-2GB log file on every host on a single day was pretty common. My biggest problem with journalctl is that, during some intensive spikes of logs, it might drop logs; we were definitely observing this behavior that some messages are clearly missing from the journalctl output, but when we check the plain log files, the messages are there. I don't remember details now, but I've read about some kind of ratelimiting / buffer overflow going on there (and somehow the part which writes to the files enjoys not having these limits, or at least having more permissive limits). So that's the primary one; I definitely didn't want to deal with missing logs. Somehow, old school technology like plain log files keeps being more reliable.
Second, at least back then, journalctl was noticeably slower than simply using tail+head hacks to "select" the requested time range.
Third, having a dependency like journalctl it's just harder to test than plain log files.
Lastly, I wanted to be able to use any log files, not necessarily controlled by journalctl.
I think adding support for journalctl should be possible, but I still do have doubts on whether it's worth it. You mention that you don't want to store plaintext logs and using logrotate, but is it painful to simply install rsyslog? I think it takes care of all this without us having to worry about it.
i use lnav in this way all the time: journalctl -f -u service | lnav
this is the ethos of unix tooling
In fact nerdlog doesn't even support anything like -f (realtime following) yet. The idea to implement it did cross my mind, but I never really needed it in practice, so I figured I'd spend my time on something else. Might do it some day if the demand is popular, but still, nerdlog in general is not about just reading a continuous stream of logs; it's rather about being able to query arbitrary time periods from remote logs, and being very fast at that.