Hi Axel,
The -analyze option activates the static analyzer component, which uses an entirely different mechanism for reporting bugs than the frontend. It should be viewed as a separate tool. The analyzer happens to use Diagnostics to output information about static analyzer reports to the console, but that's only as an aid. Fixit support needs to be properly added to the BugReport and BugReporter classes in order for the static analyzer to support fixits (as well as supporting a workflow for fixits in the static analyzer "GUI", e.g. scan-view).
I'd interpret '-fixit' as a frontend option that has nothing to do with the static analyzer. Once fixits are supported by the static analyzer, they'll be incorporated into the GUI for viewing analyzer reports.
Ted