While a reasonable idea, unfortunately, this isn't the sort of thing that can really be changed within 2.0 because it involves changing a method signature. While the calls would be backwards compatible (as it'd default to null), any class extensions that extend the constructor would fail. Now that we have reached the stable releases, changing method signatures (particularly where there may already be extensions) is something we avoid.
This would be a reasonable change for something like 2.1 though. It shouldn't be a particularly difficult addition.