Thanks for the info. The idea is to make the cost of sending the spam comparable to the cost of cleaning up the spam, which makes a lot of sense. Min TX fees can work as an anti spam measure, and can be applied without hard forking the coin if enough nodes simply refuse to relay transactions without the min TX fee.
Forgive the ignorance as i'm not a coder.
If the unconfirmed transactions UXTO are stored in the mempool, (effectively distributed cloud storage). Surely this provides the natural free market limit and restricts spam.
For example if i'm a full node or solo miner, I clearly can't store every tiny unconfirmed transaction. Therefore just limit my mempool (storage space) with a filter to a certain size, and filter on say; fee paying transactions, or only including transactions over a certain quantity of satoshis.
Larger miners, Pools or super nodes will be able to afford broader limits on their filters and store more UXTO. As enough transactions get stored in the UXTO set eventually fee market will emerge, Some transactions are worth storing until they get confirmed while others are not and should drop out.
Certain companies say NASDAQ who are just using the single satoshi as a coloured coin (hence, zero fee) will clearly have to sponsor miners to store and confirm these.
What am I missing ?
I think you are confusing UTXO and unconfirmed transactions. The UTXO set is all confirmed transactions that have unspent outputs.