This would allow wallet operations like funding transactions with smart contract-based inputs such as LN, or any input the Core wallet doesn't know how to sign for.

https://github.com/bitcoin/bitcoin/pull/17211#issuecomment-933674310
* If fee estimation does not have enough data to provide estimates, use this fee instead.
     * Has no effect if not using fee estimation
     * Override with -fallbackfee
     */
    CFeeRate m_fallback_fee{DEFAULT_FALLBACK_FEE};
     /** If the cost to spend a change output at this feerate is greater than the value of the
      * output itself, just drop it to fees. */
    CFeeRate m_discard_rate{DEFAULT_DISCARD_FEE};
    /** When the actual feerate is less than the consolidate feerate, we will tend to make transactions which
     * consolidate inputs. When the actual feerate is greater than the consolidate feerate, we will tend to make
     * transactions which have the lowest fees.
     */
    CFeeRate m_consolidate_feerate{DEFAULT_CONSOLIDATE_FEERATE};
    
    CAmount m_max_aps_fee{DEFAULT_MAX_AVOIDPARTIALSPEND_FEE}; 
    OutputType m_default_address_type{DEFAULT_ADDRESS_TYPE};
    /**
     * Default output type for change outputs. When unset, automatically choose type
     * based on address type setting and the types other of non-change outputs
     * (see -changetype option documentation and implementation in
     * CWallet::TransactionChangeType for details).
     */
    std::optional<OutputType> m_default_change_type{};
    
    CAmount m_default_max_tx_fee{DEFAULT_TRANSACTION_MAXFEE};
    size_t KeypoolCountExternalKeys() const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool TopUpKeyPool(unsigned int kpSize = 0);
    std::optional<int64_t> GetOldestKeyPoolTime() const;
    std::set<CTxDestination> GetLabelAddresses(const std::string& label) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    /**