Personally, I am not in favor of abandoning mailing lists for this type of discussion. Mailing lists have several important advantages:

• Time to respond thoughtfully: Mailing lists allow participants to carefully compose responses. Some people are naturally quick at finding the right words in real time, but others (also including many for whom English is not a native language) benefit from (or simply prefer) having more time to reflect. For example, composing this email took me 41 minutes (longer than I care to admit), a duration that would generally be impractical in a live chat room.
• Asynchronous participation and time zones: Mailing lists naturally allow people to contribute "later" which is much harder to do in chat rooms (where conversations 'moved on'). This is especially helpful for people in different time zones or those who cannot respond immediately.
• Offline processing and focus: Threads in a mailing list are ordered and easy to read offline. Chat rooms often mix multiple topics, making it harder to follow the discussion. In practice, I don't expect the majority of people to scroll back in history, which significantly reduces the potential reach.
• Engaging quieter participants: Mailing lists often generate responses from participants who do not otherwise join MUC discussions.
• Record keeping and referencing: Mailing list archives provide a single, persistent URL for referencing discussions. Chat logs are often fragmented and thus lack a canonical link.