A soft fork could introduce a new opcode, `OP_CHECKUTXOSETHASH`, allowing miners to optionally commit a deterministic hash of the current UTXO set into a block. If present, all nodes must verify its correctness or reject the block; if absent, the block is still valid. Old nodes treat the opcode as unspendable, so backward compatibility is preserved.
Because computing the full UTXO root is costly, this makes each checkpoint intentionally expensive to produce, ensuring that miners will only include them when compensated with sufficient fees. Additionally, it could be limited to one per block.
The result is a voluntary, self-limiting, incentive-aligned, fee-driven system where checkpoints are cheaply consensus-enforced when included but never mandatory.
Most nodes could operate on a rolling history validated by occasional, high-value commitments, while archival nodes remain free to preserve the full chain. This reduces the burden of initial sync and resource use without sacrificing Bitcoin’s security model, since any invalid checkpoint would invalidate its block.
In practice, the chain becomes more efficient for everyday use while the historical record remains intact for those willing to bear the expense of maintaining it.