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.

{
public:
    
    std::vector<CTxInWitness> vtxinwit;
    ADD_SERIALIZE_METHODS;
    bool IsEmpty() const { return vtxinwit.empty(); }
    bool IsNull() const
    {
        for (size_t n = 0; n < vtxinwit.size(); n++) {
            if (!vtxinwit[n].IsNull()) {
                return false;
            }
        }
        return true;
    }
    void SetNull()
    {
        vtxinwit.clear();
    }
    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream& s, Operation ser_action, int nType, int nVersion)