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.

#ifndef BITCOIN_PRIMITIVES_TRANSACTION_H
#define BITCOIN_PRIMITIVES_TRANSACTION_H
#include "amount.h"
#include "script/script.h"
#include "serialize.h"
#include "uint256.h"
static const int SERIALIZE_TRANSACTION_NO_WITNESS = 0x40000000;
static const int WITNESS_SCALE_FACTOR = 4;
class COutPoint
{
public:
    uint256 hash;
    uint32_t n;
    COutPoint() { SetNull(); }