I created an import script for chat messages from CYB Chatbox to MGC Chatbox. VBDEV contact me for it maybe you want to include it in system as well. I just imported over 440,000 messages

Without a hitch. Also Not sure if you thought about this but have a stats table to record stats of user messages so you don't have to keep 2.5 million messages and can prune delete and keep the table to set time 1 month 3 months 6 months 1 year whatever and it will prune away messages but keep stats. Let me know if this makes sense all you need to do is add a field in users table to keep a global count in for messages. Have it update every message post or just have a cron that does it or whatever it is your software. It may already be in software I saw a prune thing but not sure how it works.
We used to do contests and have anti spam built in etc for who was in top10 for chats that month
Also not sure if you have this but CYB chatbox when a user was deleted in vB it would NOT delete their chat box messages. Not sure if yours does or not but please have them linked cause the manual check who I deleted whatever and delete using manual SQL can be a pain but again up to you.
Also would be cool to see a chat post limit per usergroup. Say you want to allow registered users to view it but can only post 5 times after which it either does not allow them to view chatbox all together anymore unless they donate/subscribe and or just lock them out from posting more.