Limiting OP_RETURN at consensus level

The evolution of blockchain technology and its scalability challenges have led to discussions about the necessity and feasibility of nodes in maintaining complete historical transaction data. The current situation with blockchain nodes, especially regarding Bitcoin, allows nodes to opt for pruning, effectively removing old data to save space. This practice, while beneficial for individual node operators looking to conserve resources, raises concerns about the long-term accessibility of transaction history within the network. When a node prunes its data, it can no longer provide information on past transactions or blocks if requested, which could pose an issue if all nodes were to adopt this practice or if a user is only connected to pruned nodes.

This scenario underscores a potential future where the blockchain's growing size may necessitate alternative solutions for storing and accessing data. The choice between adopting pruning to reduce storage requirements or switching to a different cryptocurrency highlights the need for innovation in how blockchain data is managed. The absence of a consensus rule mandating the download of the entire blockchain for Initial Blockchain Download (IBD) opens up possibilities for developing more efficient methods that could alleviate the burden on nodes.

As the blockchain continues to expand, there's a risk that users may gravitate towards more centralized methods for syncing data due to convenience, despite the inherent advantages of a decentralized network. Current implementations presume the existence of at least one full archival node that does not enable pruning and thus can serve as a repository for the entire blockchain history. However, this model may become unsustainable as the blockchain grows and more users opt for pruning or centralized solutions. This situation calls for the exploration of new strategies that would allow nodes to sync in a lightweight manner without compromising the decentralized ethos of blockchain technology. Such innovations would ideally support the operation of full nodes in a pruning mode while enabling trustless synchronization of the blockchain from pruned peers, thereby ensuring the network remains accessible and robust against centralization pressures.