- Transactions could be encrypted when published as nostr events initially except size, fee rate and offer. This can be used by different clients to show them as external mempool with transactions sorted by fee rate without affecting privacy of users.
I don't think this will work because those encrypted transactions could all be fake and distort the view clients have on this 'mempool'?
- Mining pools will be incentivized to include these transaction in their blocks if they are using a higher fee rate compared to transactions in normal mempool used by bitcoin nodes or there is a mechanism to accept published offers, NIP4 is used to privately coordinate everything between user and pool. User can lock some sats in a 2of2 multisig and release it to mining pool on confirmation.
I believe you are suggesting out-of-band payment in case the fee included in the transaction itself is insufficient and CPFP/RBF is impossible or impractical? The question is why would the miner trust you to indeed release after confirmation? The 2-of-2 presumably has a clawback clause with a timeout that could be used by the user to avoid paying.
Joost