You can solve that with such a standard. Like when you're selecting the gecko engine it'll always run a Firefox process in the background, serving not just the normal Firefox browser frontend but also these WebViews. Kind of like ChromeOS does it. Of course every app will get it's own isolated browser process, but that's already the case when you open multiple tabs and it performs great.
No you won't, because it will be the same complains from Electron folks that the provided Gecko isn't the version they actually care about, and how testing is soooo hard when caring for anything beyond shipping Chrome with their application.
