Do you think people would like to have a DDS
VFO whose frequency and phase were both
direcly related to a common time/frequency
standard like WWV?

Well, no existing communication standards require independent phase
coherence between transmitter and receiver, for the simple reason that
the path length is randomly fluctuating (and there is also multipath).

As an example, if it's 3000 miles from me to you, the actual path for
HF communications is going to be somewhere between 3100 miles (a single
bounce) and 3300 miles (several bounces and a little sideways jog) or
more. With wavelengths like 20meters or 40meters, that 200 miles
represents many many wavelengths.

Tim.