This isn’t a conventional setup, but I think it might be more common than we expect.
In a project where there are two sets of instances with identical coordinates (let’s say Set 1 is the standard version, and Set 2 has ss01 activated by default), if you try to export a variable font, all instances will end up in the fvar table.
Would it make sense to have a “Keep Instances Active” custom parameter, to manually define which instances should be included in the fvar?
I noticed you recently added the “Include in fvar/STAT/static/variable” CP — is that meant to cover this situation?