Currently the only way to have a formula return Blank is by either returning an empty string ("") or by using an expression that itself returns Blank, such as List().First() (see this reply: Best way to get Blank? - #6 by artsafin).
Both feel hacky. Returning an empty string as part of a formula for a column of type Date, that implicitly gets cast to a Blank Date is awkward. I would much rather have a constant available in formulas that explicitly represents the null value in a type. Something like a Blank keywork or a Blank() function would do the trick.