The enableMajorityReadConcern server parameter defaults to true, even when using a storage engine where supportsReadConcernMajority() is false. Ideally it should default to false in such cases, however, implementing this is probably more effort than it's worth (it only affects test storage engines). Instead, storage engine creation/init should check if supportsReadConcernMajority is false and enableMajorityReadConcern is true, and handle it accordingly: either force enableMajorityReadConcern to false (if it isn't too late to do that), or else abort startup with an error message (saying that this combination isn't valid and enableMajorityReadConcern must be disabled to run with this storage engine).