Take a look a this paper: http://iacoma.cs.uiuc.edu/iacoma-papers/pact18.pdf
Its authors tested an approach (biased reference counting) to improve Swift runtime performance. The paper is short and is worth reading.
Reference counting is one of the few areas of the language that may have dramatic performance impact in our code. While not advocating for following this approach, I would like to nudge Core Team into examining strategies for improving reference counting performance.
If there’s already plans or work being done in the field of Swift reference counting I would love to learn more.