I'm aware of FUSE and used NTFS driver though it back then. So we should expect similar performance with microkernels?

It depends:) Old microkernels infamously did have awful perf because they took that context switch hit on everything, not just filesystems. I am told, though, that that was solved a long time ago and modern microkernels have fairly good performance. I'm not a kernel dev, though; you'll have to do your own research to get details.