Heads Up: ARC is introducing the new SP-20 in Fall

Me too.

Now that Fine Sounds owns Sonus faber and ARC, I believe Sonus Fabers will be the speakers of choice for the ARC listening room

By all accounts the companies owned by Fine Sounds do operate independently with the exception of Wadia which is now located at the ARC facility. In that regard, I know that they share some of ARCs administrative personnel. Hopefully, that's as far as it goes.
Having spoken to various members of the ARC working crew over the years, there was a consensus that Wilson speakers enabled the production team and the listening group to hear precisely what sounds their products were generating. ARC has kept Wilson 7s, then, I believe 8s and later Sashas as well as Maxx 2 and Maxx3s in their various listening areas.
Is it more than a coincidence that Sonus Faber (a perhaps more beautiful but slightly less transparent sounding speaker) is now in the house presumably in Wilson's place? Are there Wilson speakers in other rooms? Don't know.