Could work but seems dicey. A nick need not be registered to use IRC. Although the chathistory spec says it’s possible to get msg history for a nick, it makes no mention of nick registration. IIRC, users can use someone else’s registered nick while they are offline, no? So either it opens the door to users grabbing the DMs of others or the spec is an incomplete spec.
Even if that’s sorted, the recipient must be aware of chathistory and then know to proactively run the command to check for msgs -- IIUC. And some clients (like irssi) don’t even have the chathistory capability. I must send a quoted string to the server to use chathistory.
Contrast that with MemoServ, where only the sender needs to know how to send msgs and the recipient can be oblivious. MemoServ only accepts msgs for registered nicks. The recipient signs on and automatically they get hailed and msgs delivered.
So I probably want both. CHATHISTORY for getting a channel log and MemoServ for sending DMs with a degree of confidence that it will work.