For Symmetric FCV, on an FCV upgrade, after setFCV has enabled the target version features but before it has finished, the featureCompatibilityVersion Server parameter should return the following new format:

{version: "9.0",
 targetVersion: "9.0",
 previousVersion: "8.0"}

Note the old format should be preserved before enabling target version features, i.e.:

{version: "9.0",
 targetVersion: "8.0"}