[seL4] Proper seL4 APi/ABI design

Jumping off from the recent thread, I was curious if anyone had any thoughts about how to optimally design API's for seL4. I noticed we had a bit of info about what not to do (don't do long IPC, don't implement Posix, don't use messaging as synchronization, etc.) Are there any shining examples of what _to_ do with an API? Thanks, -Eric