I wonder about a possible solution which would be to introduce a Plot.year() helper that would read in a date in “any format” (string, Date or number), and return a (UTC) year?
Still I like @arky’s idea and would like to see an typed structure parsed to instruct they types of some element. ({typed: {'key':'type','key':'type'...})
Am going to lean towards resolving this during data preparation stage itself.
It might be very difficult to maintain a dedicated Plot.year() unless it has more advanced features for handling time series and other advanced features.