Related, non-perfectly step through documentation:
Is this even something worth supporting at all?
Define worth. Providing better instructions that help a few advanced users? Has always value to me. Patches certainly welcome.
I’d like to make https://www.whonix.org/wiki/Multiple_Whonix-Workstations#How_to_use_more_than_one_Whonix-Workstation_-_EASY easier in a sane way. Maybe some kind of auto configuration. Or wizard. Eventually using (alternative to) dhcp + whonixadvsetup to not use it - needs a lot work - low priority compared to stuff in my mind. Until I get to even think that through more and discuss it, could be a long time. And at that point it might not matter anymore. [Either because virtualizers support this use case better such as Qubes or because Qubes hosts are more widespread by then and Qubes magically isolates them better anyhow.] In meanwhile, help welcome (real difficult).
Its much easier to just tell people to run a gateway for each extra ws they want to isolate.
But then you're back to the RAM issue.
Perhaps that’s “medium difficulty”.
Easiest for multiple Whonix-Workstations:
How difficult is it to do this so that all firewall rules for eth1 are auto-duplicated for any [b]n[/b] number of internal network interfaces that the gateway auto-detects has been added to it - while maintaining complete separation between workstations on different internal networks?
Define difficult. Oh no. :) Perhaps not. :) Let's perhaps use this reference for comparison?
From a quick approximation, it’ll probably take several hours assuming the devil is not in the details what I find more likely here.