Flutter is just an open source project. You are certainly welcome to use it (and maybe even contribute to it), but it isn't in any way something that Google wants to force anyone to use. We hope people like it and want to use it, that's all.
Uh, really? So then you either have no plans to try to make Fuchsia OS a major commercial success? Or, do you plan to offer multiple first-class-citizen ways to write native apps on Fuschia, not just Flutter/Dart? Because if the idea is to make Fuschia the next Android and Flutter the official native app platform, then sorry but your comment is a little wilfully naive.
Fuchsia doesn't require using Flutter. Flutter is just one possible UI framework you can use with Fuchsia.
What are others? Will there be first class Kotlin support?