Just wanted to add a couple of comments here in case there's any interest. In our missions to make the world's market data available we deal with financial exchanges, many of whom are already recording event data at nanosecond resolution.

Further, I believe the decision to use a separate nanoseconds field to be essentially correct. While  it may well introduce some arithmetical complexity its value in backwards compatibility should be regarded as paramount. If I understand it correctly, the new nanosecond resolution times would continue to be correctly handled (module loss of nanosecond resolution) when handled as current microsecond date-times.