Hi,
I don't think custom fields show in reports because the report columns are not yet configurable. You can however access your custom fields in a report using the Filter > Custom Query > Test Plan > [select your custom fields]. The only workaround I can think of is below. Normally I'd suggest using the report export to dataset feature but that doesn't export test plan data:
Create your report and give it a title that contains the custom field criteria. It's then possible to tell what the report is about and what criteria is being used to generate it. After you've run the report, copy the URL and search for your custom field criteria. You can quickly create more reports by changing/replacing the criteria in the URL and pasting into a browser.
