Technical reasons. To avoid modifications, because, see below…
Possible in theory but better to keep modifications to Tor Browser as minimal as possible for better stability and easier review since lots of Tor Browser issues are already falsely attributed to Whonix.
Modification of Tor Browser would further add to the confusion.
Messing with any files inside Tor Browser has potential to break it or break its internal updater. At very least, consequences would take time to research. More stable and time efficient o just keep it as is.
Yes, Tor doesn’t run on Whonix-Workstation. Therefore that file has no effect.
“Ephemeral” Tor onion services. Creation (and re-creation) of such onion services is started from inside Whonix-Workstation. A Tor aware application will use Tor control protocol commands to create it. The key is either discarded (temporary onion services) or retained by the application (restartable onion service with stable onion domain name). An example application is OnionShare.
Should be, because…
Whonix does not modify Tor.
Should function the same.
ClientOnionAuthDir should function similarly.
See https://www.whonix.org/wiki/Free_Support_Principle - i.e. find out how to use this in an easier environment first. For example on non-Whonix, non Qubes. For example on Debian
buster. If it works there, replicating the same in Whonix should be simple.
I don’t think
ClientOnionAuthDir can be used in Whonix-Workstation.
Whonix-Gateway only. Because it is a Tor config file based configuration.
Ephemeral Whonix-Gateway ™ ProxyVMs
Use ephemeral Tor onion services using Tor control protocol.
But still notice the forensics related warnings on https://www.whonix.org/wiki/Qubes/DisposableVM.