An attempt to create a wildcard index under FCV 4.0 with a 4.1/4.2 binary, mongod returns the following error:

{
    "ok" : 0,
    "errmsg" : "Unknown index plugin 'wildcard'",
    "code" : 67,
    "codeName" : "CannotCreateIndex"
} 

We should change this error to state that featureCompatibilityVersion must be 4.2 to create a wildcard index.