There's a cloud based IRC client called, simply enough, IRCCloud, that essentially acts as a remote client, keeping you logged into your IRC servers at all times, so that when you return you can just open up the app on your end and see them all

You can slap someone with a trout.

I think XMPP is a much more complex protocol... particularly compared to IRC. Because of this, find good XMPP clients, particularly terminal or CLI ones is hard (nothing close to weechat anyway).

Likewise, from my experience, XMPP has mostly been used for direct or individual messaging and not for group chats like IRC has. I understand that it can be used for group chats (I was in one for a while), but there are many more well known IRC channels than there are XMPP group chats.

There's also a newer federated chat (plus VoIP signalling) protocol called Matrix that's worth a look.

One feature that sets it apart from XMPP is its support for multi-client synchronization: if you log into the same user account from multiple clients (e.g. where one of them is a desktop app and another one is a smartphone app), your chat history will be synchronized across them. Or as one of the Matrix developers put it: "XMPP is all about message passing, whereas Matrix is all about state synchronisation".

On the downside, though: although the Matrix protocol is designed to support presence-status, it seems that many (?) of the public Matrix homeservers have that feature disabled for performance reasons.