Miranda is very good, six long years together, but seems that her possibilities are coming to its end…
Profile weights over 150 mb, history of some contacts opens for about 2-3 minutes. Somewhat annoying.
So, we need a scalable multiprotocol instant messenger.
No need for blackjack and hookers.
Need support for (comfortable working with) > 500 contacts, > 30000 messages per contact, metacontacts (different addresses of the same user), Jabber, ICQ, MSN, IRC. File transfer is mostly irrelevant.
Ability to work through Socks4\5 and HTTP(S) proxy, is a must, support for plugins/APIs is good.
Profile encryption is not required, but would be good, too.