Dust Expiry: Clean the UTXO set from spam

The growing issue of UTXO set expansion due to spam activities has led to the proposal of a soft-fork aimed at introducing an age-based expiration for dust outputs, a measure designed to address and mitigate the clutter within the UTXO set caused by spammers. This proposal emerges in response to the significant growth in the UTXO set size, which has seen a doubling since 2023, from 4.6 GB to 11 GB, largely fueled by inscription spam attacks, BRC-20 token scams, and wash-trading. The current state indicates that approximately half of the UTXO set might be attributed to spam-related activities.

Unlike auxiliary transaction data spam, which can be managed to some extent, UTXO spam is permanent and cannot be pruned, presenting a more severe problem. The proposed solution involves implementing a rule whereby very small and very old outputs become unspendable once they reach a certain age threshold, defined by the formula utxo_amount T * dust_limit. Upon reaching this state, these expired UTXOs could then be effectively removed from the UTXO set, thereby cleaning up and reducing its size. The proposition seeks community feedback to refine and possibly implement this approach as a means to combat the spam issue plaguing the UTXO set.