^^^ Interesting thought about an unlimited number of machines running with VEP 
Though I’d have to have an uneducated guess that there would be a limit with the number of VEP slaves ‘somewhere’ due to the above proposed potential hardware/software limitations…VEP coming with 3 or 4 licenses I believe, should be well more than enough for anyone’s needs with that many 64 bit machines. The company charges more for ‘additional’ licenses, so I’d have to think it would be a safe bet that at least somewhere ‘more than’ 4 machines can easily be ran.
I know of a guy on another forum that runs I believe 6 machines, all ‘synced’ together. That’s just crazy 
And he can run PC’s, Mac’s and whatever DAW software’s he wishes, Mix N’ Match.