From what you are saying, you are asking Limewire and Bearshare to add support for chatting through IRC, which has pretty much nothing to do with the Gnutella Protocol (just to make that clear).

Actually technically, gnutella is a distributed search engine, to download files is like downloading from an HTTP server, and that is why some support an built in mini HTTP server. So searching is distributed and downloading is peer to peer. I would think it would be interesting to create a search engine for users and chat rooms.

IRC in the long run may not that good of a solution beyond Gnucleus, I think (not sure). Because there are thousands of gnutella users, imagine thousands of gnutella users going into a single chat room (#gnutella/chat), I'm not sure if this causes fragmentation or a room to be split (to handle the multiple users), but that would mean you would lose contact with your friends. Having that many users chatting in the same room is not only confusing but also does affect the bandwidth as each person sends a message and that message gets sent out to each user. Plus IRC is a centralized system, that is subject to fallouts of being a centralized system, that is if the IRC server you are connected to finds that it can not handle the capacity of the number of users it will not accept any more users, and if the server is attacked by hackers or has some financial issues and has to shut down, then everyone has to go through some problems and the gnutella clients have to take that into account by diffrent means. But if this is the ideal way to do this, then why bother? If someone really wants to chat on IRC they can just start an fully featured IRC program of their preference.

A more interesting way to chat, is to chat with a person who you are sharing a file with or are going to share a file with. This way people of common interesting can start a conversation with each other, but that is not IRC, that is like ICQ/ AIM type messaging, or it could be set up so that you can create your own chat room, and people who download from you can start chatting in that chat room, or even allow linking chat rooms, so if I am running a chat room I can connect my chat room to someone elses. But my point is that there is more interesting things that can be done that are a bit beyond the scope of IRC. These may be possible using the IRC protocol or other (although I find IRC to have certain limitations).