I wish I could pop out chats in #Slack. I want all my active chats visible at once. It's really easy to lose a conversation when I have several going at once, or I'm waiting for a reply that might not happen for hours.
I consider my Slack/IRC gateway the best one out there, at least in terms of looking the most native to IRC users. We use this to connect the #indieweb IRC channel with our Slack team, so people can join the same rooms from either Slack or IRC. Often times people don't even realize that other users in IRC are actually connected via the Slack bridge! However, one glaring missing feature was that image uploads from Slack did not come through right. Today, I fixed that!
When someone types an emoji in Slack, it shows up in the API as a text description surrounded by colons. For example, 😻 is :heart_eyes_cat: when it comes through the API. Previously, the gateway would just send the text through to IRC, which doesn't look great for IRC users.
For quite some time, we've been running my IRC/Slack gateway so that our main #indieweb IRC channel is also available in Slack. It's great because it allows people to use the nice mobile-friendly Slack client, while also not locking ourselves into a proprietary platform. The bridge is also used to allow people to join the chat from our web interface.