Yes, that's a big problem.
It's quite simple really. With WinRT (and iOS) you do not decide what you can and cannot run. Microsoft (and Apple for iOS) decides. It's pretty much against all that is OpenSource. Which is "freedom", freedom to do, run, modify, what you want.
Finally there is a very simple reason why I'm very much against this development of requiring everything signed. It would have made it impossible for a project like Cura to get of the ground. It started in my free time, without any resources. I could just put releases on the web and people could run those. That's how initial development starts for small open-source projects.
EUFI and how it's implemented by WinRT kills this development cycle.