I'm not sure why no one has thought of this before, but I can't think of a single downside.

Never change a running system. Perl 6 developers communication via IRC, Mails, Code (via svn), phone calls and in real life - so far nobody complained that any of those were ill suited, and using a different network might improve that.

Not requiring irssi for communication with the perl community means one less process running and less stuff stored in ram. I've talked to quite a few people in the perl community who are currently forced to use both programs simultaneously. This is not a good long term solution.

The Unix philosphy is "one tool for one job", and many perl hackers like it that way. I like it that way.

IRC is an open protocol, you can enhance your program (whatever it is) to understand IRC (if your program isn't open source, that discussion is moot anyway - you don't force open source programmers to use closed source software to communicate. You don't. Period.)