@ - Right, the fork doesn’t support multiple signed in Live users at the moment. It’s worth noting that even if we added this it would really only apply to UWP on Xbox. UWP on desktop PC is inherently single user, with the Live user identity coupled to the signed in Windows user.
On PC you need to use the Xbox App to switch profiles (this goes back to that tie between the Windows user and the Live user). You could potentially present a button to launch the Xbox App to streamline this a bit.
@shop_0761 - The MR folks are not typically very active here. I’d suggest asking your questions directly on the linked issue.
@ - I haven’t tried to use the Substance plugin specifically, but I’m fairly familiar with getting things working in UWP in general :). If you’re able to share more details it might turn out to be something I can help with.