What you are telling me is that you don't see how not supporting subaccounts breaks these clients user experience. That's fine, but I am telling you, it will suck for them. It will become very confusing if this becomes highly used.
I am saying this because the average Amethyst user has 2+ independent accounts logged into in the same phone. So, I know people will use this if you develop it. The difference is that with Amethyst they are different personnas. They generally don't share the same name or picture. So, It doesn't break the user experience. It's a clean separation.
But they are not different, it will be very confusing for those not implementing it.