Consumers pay for iOS, but Apple still bans you from selling your app in the store.

The gatekeeper function of the platform means they can shut you off at any time.

If instead, Slack published a protocol so anyone could author a client, then bots would just be normal chat users, for the most part, on par with regular users, and a bot would simply be something you deploy somewhere to sit in your channels, just like IRC bots.

I think Slack is a great app, very good UI, but I'm a little sick of proprietary messaging. We really don't need proprietary centralized messaging networks. Standardize a federated open protocol and let people compete on the clients and let the community agree on extensions to message payloads that clients pay attention to, or ignore.