Using NIStune will retain auto gearchange logic, saving unneccesary pressure on drivetrain, without compromising on tune by using piggyback.
You will also retain knock maps which are a feature of the stock ecu, which Power FC does not have.
I believe a few tuners over here in the West are taking up NIStune, but I know Top Racing have for a fact.
note: VCT can still be activated by an RPM activated switch(or similar) if going the RB20 ecu route