IRC has some advantages. You can use with without specialized software (and I have done many times when not having a IRC client), or you can write your own IRC client or use one of many. There may also be web interface if you want them.
Note that you can make IRC server which makes logs of channels and could provide a link to access the file in the MOTD or HELP file, if desired. It can also be done by clients and link in the TOPIC message, which is more common.
IRC is good for fast communication with short messages, but for slow communication with long form messages is also sometimes more useful and for that, NNTP would be better, I think.
Note that you can make IRC server which makes logs of channels and could provide a link to access the file in the MOTD or HELP file, if desired. It can also be done by clients and link in the TOPIC message, which is more common.
IRC is good for fast communication with short messages, but for slow communication with long form messages is also sometimes more useful and for that, NNTP would be better, I think.