@pganssle - let's keep the substantive discussions in the tracker so that they are not lost on github.  You wrote:

"""
what is still blocking / needs to be done on this? Beta freeze for Python 3.10 is coming up at the beginning of May and I think we may have enough time to get this in before then. Probably would have been better to get it into an alpha release, but if we miss beta freeze it'll get pushed to 3.11, and I do think that nanosecond support is a desirable feature for a lot of people.

It might be good for us to get an explicit "to-do" list of concerns to be addressed before this can be merged.
"""

I don't think full nanosecond support is feasible to complete in the remaining weeks, but we can try to add nanoseconds to timedelta only.  The mixed datetime + timedelta ops will still truncate, but many time-related  operations will be enabled.

I would even argue that when nanoseconds precision is required, it is more often intervals no longer than a few days and rarely a specific point in time.