This was never enough for me. On paper Pidgin did the trick, but you still had to remember which of your friends preferred which platform, you had multiple "friend" entries for the same person, many used silly pseudonyms that they certainly didn't go by IRL, you had no way to tell if your friends actually were monitoring each of their accounts (I uninstalled aim months ago, have you been sending me messages on it?), you couldn't have group conversations across networks without mental gymnastics or compromise, the features offered on each platform were inconsistent, both on their native apps and the features pidgin actually implemented.

That to me is not universal chat, that's just welding 10 chat apps into one, somewhat poorly.

That being said XMPP was well on the way to becoming something universally supported, and though the protocol itself was way more complicated and crufty than I'd like, it's a shame that Google particularly abandoned it for really no reason.