Toke,
I just realized something else and did a quick test.
Initially, I was not seeing ProRs 4444 as an import or transcode option. ProRes 4444 only seems to be supported when your project is set to RGB. In FCP, it is supported in both RGB and YCbCr projects.
I you try to import into a ProRes 4444 file into a project set for YCbCr you will only have the other flavors of ProRes available, and you will not get a Fast Import, as you will be transcoding.