While it is a bummer there is no OLE DB or ODBC drivers for 64-bit Microsoft Access connections (.accdb)... Microsoft does have a 64-bit version of the Access Database Engine (and of the Office application itself). I'm sure it is no simple task and a different approach than before, but I don't see why ESRI cannot use the 64-bit ACE drivers?
The loss of Access database connectivity is HUGE. I just heard that ArcGIS Pro 2.0 was considered to have feature parity with ArcMap... but without this greatly important feature we cannot claim that ourselves. Engineers love Access (and Excel) and not sure this is a limitation we can even work around.
Thanks for the consideration.
*UPDATE: Bruce also mentioned the idea of "Interoperability Connections" with the Data Interoperability extension that currently exist with ArcMap but not Pro. If a more real-time, non-static ETL option, could be achieved with this that could also be an option.