A good and robust bot api and useful smart widgets based on url are a must. I've had chats go from discord to matrix and then simply die after a few days.
Matrix's bot support should be excellent? It's arguably more robust than Discord's given it's an open API and there are tonnes of SDKs and bots building on it: https://github.com/turt2live/matrix-bot-sdk, https://matrix.org/docs/guides/usage-of-matrix-bot-sdk, https://github.com/bnjbvr/botzilla, etc.
What do you mean by 'smart widgets based on url'?