For anyone else landing here and interested in API design, I wanted to share some more helpful resources courtesy of @zinggi:
This post lays out guidance for contribution the most clearly of anything I’ve seen: Building Trust: What Has Worked
This talk from Evan is helpful too: https://youtu.be/DSjbTC-hvqQ
Here’s a podcast interviewing Robin, someone not on the core team who contributed to core: https://elmtown.audio/elm-019-improved-collections-robin-heggelund-hansen
And finally, if you’re still up for designing an API, there’s a Slack channel for that: #api-design