Mike presents an update to the Hourglass protocol on the Bitcoin dev mailing list. Hourglass addresses P2PK coins, the earliest mined coins vulnerable to quantum attacks. These coins, including Satoshi's, total about 1.7 million BTC. There are two camps on what to do with these coins: do nothing, or confiscate. The original Hourglass proposal restricted PPK spends to one output per block. Someone with these coins can still spend it, but it is just inconvenient. Hourglass V2 mandates that any outflow from a transaction with a P2PK input exceeding one Bitcoin must send that amount minus one back to the original sending address.
This would lead to increased block space usage and a new fee market. Hourglass V2 offers a more gradual restriction, appealing to both confiscation and liquidation camps. Miners can still be paid fees, potentially incentivizing quantum attackers to subsidize Bitcoin. A flag day activation soft fork would precede implementation.

Sound approach to fixing the quantum issue!