Yes, it worked for me in I2C mode. However, I found what seems to be a fatal firmware bug, as follows.

At the end of the wake period the DFR goes to sleep, as expected. However in doing so it sometimes pulls the SDA and SCL lines low and doesn't release them.

This not only crashes the DFR and any other I2C devices on the I2C bus but it is unrecoverable without a DFR power-reset.

I tried various software techniques to keep the DFR permanently awake; but alas, they all failed.  Any extensions of the wake mode seems timeout seems to depend only on the receipt of a valid voice command whist the module is awake.