A couple of things. First, it would be helpful to know more about the potential loss of advance seat selection in UC. The ability to select a seat in advance should be a basic element of any business class experience. It would seem crazy to lose it - what is the possible advantage of that? If VS is removing that, they will lose my business. The bar is still right on top of the cabin in the non-revamped UC and there is no way that I would fly VS again if there wa any risk that I would be within five rows of the bar.
Second, my guess is that even if they allow mobile use, it will be outside UK airspace. BA allows use of pax mobiles for e-mail and texts on its LCY-JFK flights, but that service is not available immediately after take-off. IIRC they switch it on some time after the flight has left Shannon. I note also that although they presumably could allow voice calls, they have decided not to. Long may that last.