{ field: { eq: Regex } }

is not supported ATM as it will always end to 

{ field: Regex }

 for matching the regex.

Specifying the $eq
operator is equivalent to using the form { field: } except when the is a regular expression. See below for examples.

The current behavior for find(field, new Regex()) should stay the same (matching the regex), but find(field, '=', new Regex()) must generate

{ field: { eq: Regex } }