I think an inheritance system would be better. Any kind could extend a simpler kind that has easy to render fallbacks if the client doesn't know how to deal with the more complex kind.
What do you think of the idea discussed at the beginning of https://www.youtube.com/watch?v=kk1x0Bjtes8 about creating a new short text tag that can be added to any weird new event kinds so clients that don't support these kinds can render that as a fallback?
I think an inheritance system would be better. Any kind could extend a simpler kind that has easy to render fallbacks if the client doesn't know how to deal with the more complex kind.
Not a bad idea.