That couldn't work securely. The problem with it would be that when cbstream is down, another irc user can log in with that nick, and if someone sends a message to cbstream at that time, that user would immediately get that message. What's worse, even if a user would be so careful as to check that the real cbstream bot is up before he sends a message, he couldn't do that without a bad race condition, because an impostor could watch the #cbstream channel for when the cbstream bot dies, and when it does, change the nick of another irc connection to the server to cbstream immediately.

The alternatives to the current solution are the following. The code for the previous login mechanism (using memoserv) could be improved a bit, but that seems to be a dead-end to me. A separate html form you access on http could be used to log in. Finally, I could use a channel that you can write without joining (which is very similar to what you mentioned), but because of a limitation in the irc server freenode uses, this can only be made work if I made the channel invite-only so no-one but the bot joins it, and I feel this would be a bit less convenient than the current method.