- general chat
- official announcements
- webhooks to main project
- FAQ static channel
- Guild/Alliance list static channel
- private channels
- public channel for recruiting
- lots of custom channels
3rd Party Project Server
- support channels
- project github webhooks
If we had a structure like this, discord would make sense. However, Screeps by nature is not very alliance based, and "3rd party projects" account for over 80% of the traffic if that includes shared code relating to the game.
This is a game about programming, and slack's channel structure accommodates that. If we wanted to emphasize the "social network" aspect of the game, or alliances, maybe discord would work for that. But, at the moment, that's not what the community is about.
If we're talking about alternatives, and if at some point we decide slack's history is a killer (which it semi-is right now), I'd agree with SemperRabbit about https://riot.im/. Matrix has the advantages of IRC that @vrs and others have mentioned of being a free protocol, and with riot.im hosting we'd also have scrollback and other features slack provides over IRC.