The user of-course can already implicitly work out this information from comparing the fee-rate with the actual fee.

I think that it would be useful for people not wanting to do this arithmetic in their head.

SerializeTransaction(*this, s, ser_action, nType, nVersion);
        if (ser_action.ForRead()) {
            UpdateHash();
        }
    }
    bool IsNull() const {
        return vin.empty() && vout.empty();
    }
    const uint256& GetHash() const {