I guess a SQL Server expert will need to interpret
https://blogs.msdn.microsoft.com/sqlnativeclient/2008/02/27/microsoft-sql-server-native-client-and-microsoft-sql-server-2008-native-client/ and say exactly which SQL Server versions require the legacy datetime handling. I see django-pyodbc-azure still supports
Microsoft SQL Server 2005 (end of extended support was April 2016) and SQL Server 2008/2008R2 (end of mainstream support 2014, end of extended support July 2019). If those are the only SQL Server versions that don't have microsecond support, django-pyodbc-azure might consider dropping support for them -- doubtful if those users require the latest version of Django, I'd guess.
I'm not strictly opposed to keeping the supports_microsecond_precision feature around if it's helpful for that backend, but we'll need contributions from django-pyodbc-azure maintainers to keep it updated (mainly with respect to using the feature to skip or change behavior in tests).