Personally I don't have a problem with priority fees as long as there's still room in the blocks. But when blocks are full it could lead to weird situation when high fee txs are stuck en masse while low/zero fees txs are going through.
Weird situation? Sounds like a normal situation to me. It's exactly what I expect to eventually happen. Lots of very small fee (or zero fee) transactions will be confirmed in blocks because the miner was paid to confirm them in a separate transaction.
And going back to my original question. In the event of blocks being notoriously maxed-out (aka fee market), if the "priority txs" form noticeable % of total txs volume, would it be at all possible to accurately estimate fee needed to get confirmation within next few blocks, or will it be totally guessing game?
There is no way to know how much the miner got paid for their effort. Therefore, if you don't have a contract with the mining pool, and you aren't sending your payment to someone that has a contract with the mining pool, then it wouldn't be possible to "accurately estimate fees needed to get confirmation within next few blocks". You could pay a fee higher than the highest fee in the block, and still not get confirmed if the pool completely filled the block with contracted transactions.
In other words, if services like bitcoinfees.21.co (or wallet providers) predict optimal fees based on txs confirmed in the last X hours - and if they can't distinct between normal and prioritised fees, that could make their predictions pretty useless.
Yep. They would need to receive information directly from the pools as to what fee they would require to get into a block, and then they'd have to trust that the pool wasn't lying to them. I suppose they could create a large number of their own transactions, and then watch to see which of their transactions confirm, but that could get a bit expensive.
Am I missing something or is it yet another flaw in the 'fee market' model?
Flaw? Feature?
Toe-May-Toe? Tah-Mah-Toe?
Capitalism and free-market at work. Is it a good thing or not?