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.
},
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return NullUniValue;
    LegacyScriptPubKeyMan& spk_man = EnsureLegacyScriptPubKeyMan(*pwallet);
    LOCK2(pwallet->cs_wallet, spk_man.cs_KeyStore);
    std::string label;
    if (!request.params[2].isNull())
        label = LabelFromValue(request.params[2]);
    int required = request.params[0].get_int();
    
    const UniValue& keys_or_addrs = request.params[1].get_array();
    std::vector<CPubKey> pubkeys;
    for (unsigned int i = 0; i < keys_or_addrs.size(); ++i) {
        if (IsHex(keys_or_addrs[i].get_str()) && (keys_or_addrs[i].get_str().length() == 66 || keys_or_addrs[i].get_str().length() == 130)) {
            pubkeys.push_back(HexToPubKey(keys_or_addrs[i].get_str()));
        } else {
            pubkeys.push_back(AddrToPubKey(spk_man, keys_or_addrs[i].get_str()));
        }
    }
    OutputType output_type = pwallet->m_default_address_type;
    if (!request.params[3].isNull()) {
        if (!ParseOutputType(request.params[3].get_str(), output_type)) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[3].get_str()));
        }
    }
    
    CScript inner;
    CTxDestination dest = AddAndGetMultisigDestination(required, pubkeys, output_type, spk_man, inner);