[BIP Proposal] Limit ScriptPubkey Size >= 520 Bytes Consensus.

The discussion initiated by Tom Harding on the Bitcoin Development Mailing List touches upon the potential implications of implementing a scheme aimed at reducing the size of the Unspent Transaction Output (UTXO) set through Merkle Hash Tree (MHT) tracking. Harding points out that such an approach might result in a significant increase, approximately 10%, in the UTXO set size. This could necessitate a comprehensive resynchronization of pruned nodes from the network and a full reindexing of unpruned nodes, which might lead to extensive downtime, highlighting the operational challenges associated with this strategy.

Harding further elaborates on the ineffectiveness of this method for UTXO set size reduction, given that outputs exceeding 520 bytes do not constitute a large portion of the existing UTXO size. Therefore, integrating MHT tracking could ultimately fail in its primary objective. Moreover, there's a possibility that this change could inadvertently create a new class of scarce assets, particularly transaction outputs consisting of "primordial coins" not subject to the new rules. This aspect could attract interest from NFT enthusiasts looking for unique assets, potentially leading to unintended consequences for the Bitcoin ecosystem.

The conversation also delves into broader concerns regarding the direction of proposed changes to Bitcoin's protocol. Harding is skeptical about proposals that go beyond merely limiting script sizes, as these could introduce more severe issues. He suggests that while restricting output sizes may not directly harm any specific interests or usages, it does not address the underlying economic behaviors driving certain groups, like NFT collectors, who value high transaction costs for their scarcity and value implications.

In essence, the discussion raises critical considerations about the technical and economic ramifications of proposed modifications to Bitcoin's functioning, including the risk of enabling the creation of new asset classes that could diverge from the intended purpose of such changes. The debate underscores the need for a nuanced understanding of the diverse motivations within the Bitcoin community and the potential impact of technical adjustments on those dynamics.