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LimeChat on the Mac supports both of those features. I'm sure there are other clients that do as well.

And for history, there are plenty of history bots that have web searchable archives of IRC channels.

Weechat with Glowing Bear does too but it needs to be set up.

IRC already has these, its just a matter of packaging it.

FWIW irccloud is a lot like slack but for IRC, they offer "team" accounts and hosting. No search, though.

and chat history

How is this not possible with IRC? Channel log bots have been around for yonks.

Only Slack's integrated view of history is acceptable to nontechnical users. Also to technical users like me who don't want to mess around maintaining and talking to bots.

I believe the dismal UX in your suggestion is the reason Slack is popular. By contrast, "it just works" and it works consistently across all communities, making for a compelling product.

You can get that with weechat + screen + glowingbear.

Or with an IRC bouncer but we're well beyond what I would expect anyone non-technical to set up.

Textual 6 supports inline images and chat history.