That provides all the freedom of the Apache license while adding a clause that would prevent big cloud companies from monetizing the project.
We offer consulting services and premium addons for the Chat SDK. The add-ons include things like: typing indicators, read receipts, video and audio messages etc... We give 90% of the chat functionality away for free and our customers are free to develop this functionality themselves if they wish. However, for a small licensing fee they can get robust well tested addons instantly.
The core Chat SDK will always be free and open source. We are planning to support the code until at least December 2022.
We have tested the Chat SDK with 300,000 daily users and it works perfectly. That's with over 2 million monthly users! Really, Firebase is the only limitation in terms of scaling and Firebase can support millions of daily users.
Firebase uses a no-SQL database so it doesn't have a predefined schema. As the app runs, it will generate the schema as it goes. The schema is very flexible - you can add extra custom data if you like. As long as you don't remove fields, the Chat SDK will run correctly. If you're interested in the schema you can check out the Firebase Schema Guide.