Does this affect the waiting time to get low-fee but above minrelaytxfee transactions cancelled and return them to our wallets? From my understanding, unconfirmed transactions will be back to the sender when they are dropped from the mempool of most nodes if they are not mined at all. And it usually takes a few days now.
First of all, transactions are not "canceled" nor "returned". When your wallet forgets about a transaction, nothing is sent back, it simply acts as if the transaction never happened.
With my little knowledge, it seems some users will have to wait 2 weeks rather than 72 hours and they can't expect the transactions will be evicted due to the restart of nodes after 0.14. I'm not really sure as I also heard some nodes/wallets rebroadcast the transactions constantly and it makes the mempool expiry time little or nothing. (then why those transactions are back to the sender only in a few days.)
I know I can send RBF transactions or CPFP or sometimes doublespend even without RBF flag but i'm just curious because most users don't know how.
The previous expiry time was 3 days. However, often times transactions will either expire out of the mempool and be rebroadcast and subsequently put back into the mempool, so the expiry time did not matter at all. If your transaction is unconfirmed for more than 2 or 3 days, it will probably get evicted from the mempool anyways because the fee is too low. The minrelay fee has been changed to be dynamic for a couple of releases already. If a transaction remains unconfirmed for several days, its fee is likely too low and the minrelay fee will have moved to be greater than that transaction's fee rate so it is evicted anyways. Transactions that pay a sufficient fee will probably confirm within two or three days so this does not really affect that.
