I think there's a huge potential for developers on chat platforms due to the fact that the app is already installed, and the user is already "logged in", and the UI paradigm is more or less standardized across OSes. I worry though that this opportunity will be squandered by the big social platforms by botching the bot discovery mechanisms, much like the app stores did.
A problem is that there are so many chat apps and it's hard to support all of them. There are some cross platform development tools (and online services) but some chats have different ways of interaction. It reminds me of the cross platform GUI toolkits of the 90s. They worked pretty well but they were never the same of the native UI so nobody was happy.