I guess this is because of the amount to be broken down into smaller transactions, i.e. 123.4567 => 100 + 20 + 3 + 0.4 + 0.05 + 0.006 + 0.0007. I think this way will increase number of inputs enormously. If this is corrent, Monero need some serious improvements otherwise it will be struggle on getting more adoption from users and exchanges. We can't tell user to send coins in even amount of something like 100 XMR instead of 100.123456789 XMR.
We can't expect every pool to raise limits for the good of network, is an update needed at protocol level for this task ? I thought recent mandatory update with new fee was about to fix "dust transactions" problem ?
Larger mixing count -> bigger transaction.
The transaction size limit is not hard coded in the protocol - it's adjusting by itself, so it depends on the users:
More larger transactions close to the limit -> larger transaction limit -> bigger blockchain.
The transaction fee is currently hard coded, so whatever the transaction size -> same fee - this will be changed to larger transaction size -> larger fees.
We could expect the pools to raise limits - the same way they do it for Bitcoin, because sending you dust, which is more expensive to spend then the dust itself is not good for the users and they'll eventually leave the pool if this is not changed.