P2Q: SegWit version 3 spending rules

A draft Bitcoin Improvement Proposal by Casey Rodarmor for "Pay-to-Quantum-Safe" (P2Q), defined as a SegWit version 3 output. Today it behaves identically to Taproot (BIP 341/342), so it requires no new signature scheme to deploy.

Its distinguishing idea is optionality: because the output type is segregated, a future soft fork could disable key-path spending for these outputs alone if elliptic-curve cryptography were ever threatened, forcing script-path spends without affecting existing Taproot users. This contrasts with BIP-360, which removes the spendable key-path commitment from the start.

As of 2026 it is an early draft, not a scheduled change, and like BIP-360 it leaves the choice of post-quantum signature algorithm to future work.