Would it be completely unreasonable to allow `fundrawtransaction` to use unsafe outputs?

I understand this means the resulting transaction may be invalidated whenever the unsafe output I'm relying one disappears (e.g. because the transaction that produced it was RBF-ed) but in my case that's ok, I'll react to that and re-publish the tree of child transactions accordingly.

But let me know if you think that's too much of a footgun for users, in that case I'll architect my solution differently.
{
    std::vector<CTxOut> txouts;
    for (const CTxIn& input : tx.vin) {
        const auto mi = ->mapWallet.find(input.prevout.hash);
        
        if (mi == ->mapWallet.end()) {
            return std::make_pair(-1, -1);
        }
        assert(input.prevout.n < mi->second.tx->vout.size());
        txouts.emplace_back(mi->second.tx->vout[input.prevout.n]);
    }
    return CalculateMaximumSignedTxSize(tx, , txouts, use_max_sig);
}
std::pair<int64_t, int64_t> CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *, const std::vector<CTxOut>& txouts, bool use_max_sig)