Have you found incoherences in the APIs? Does an interface-specific registry needs refactoring or is hard to use? Is a device driver missing options? We are now planning v3 to polish the APIs. This is a major release which will permit small breaking changes, as defined by the compatibility guarantee.
Now is the time to report these issues and voice your opinion! Please file a bug or reach out on #periph on the Gophers slack. You can find the slack invite on the top right of this page.
It is slated for around Q1 of 2018. It is not an hard date, we will release once we feel we reached the desired polish level. You can view the currently slated changes via the API breaking label.