The AutoDateFormatter handles the tick labels in a sensible way, but by default it is used for the data readout (e.g., Axes.fmt_xdata). As a result the data readout is highly discretized rather than quasi-continuous. This should handled automatically by dates.DateConverter specifying a suitable alternative formatter for the readout in the AxesInfo object it provides. This requires expanding AxesInfo and everything working with to support this additional (optional) information.

In the case of datetimes, one approach for the readout would be to use floating point instead of integer for the least-significant element of the tick format string. For example, if the ticks are formatted as integer year-month-days, the readout could be the same but with floating point days, perhaps 2 digits after the decimal.