Only for future releases. If it works currently for iOS 12, it'll keep working for those builds of iOS 12. I fail to see how Apple can break what already works for code they can't/won't change.
Wrong. There are people who would like hardware kill switches but are required to run either iOS or Android apps for work. With iOS in a VM, you could truly "log out of work" and shutdown that part of your phone when not needed without carrying a second work-specific device.
And they would not want to do that on a Librem phone. Librem phone is for the tiny subset of people who want a computer with a free BIOS as well as a fully-free Linux distro like PureOS.