Core Infinity board

[Confused]

Will it be possible to fit the Wi-Fi and Duet boards removed from the Master to make way for the new streamer board into the Companion and, with another remote control, effectively have two 220 Pros?

Oddly enough I was thinking exactly the same thing.  The answer to the above has to be yes.  So however good or bad the new OS board turns out to be, it does at least offer the option in the future of repurposing a dual mono as two stereo masters.  At least it's something!

The firmware to set the new board could easily deny the use of the old one.

Agreed.  Although I can't see why Devialet would want to do this.  After all, I suspect many Pro users will never fit the new board.  This will depend on individual users, but why fit something you will never use?  Especially if it has the potential to add noise or any other similar negatives.  Although if Devialet did indeed do this via firmware, then you could still use your second 'master' with old firmware.