While usually people using AIM are relying on a standalone client of sorts, for people who travel a lot or go from machine to machine they might find it very useful. The function is already available, and via the chat menu inside Gmail you can login to an AIM account. Some Gmail-specific features, like organizing chats into conversation threads, are brought along with this addition.
There are certain disadvantages, such as needing to re-enter your password every once in a while (though not on every login attempt), but for someone who may not have access to an AIM client it could prove to be very handy. There's no mention if they plan on incorporating other chat services to Gmail in the future.