[bitcoin-dev] Hardfork to fix difficulty drop algorithm

We are coming up on the subsidy halving this July, and there have been some concerns raised that a non-trivial number of miners could potentially drop off the network. This would result in a significantly longer block interval, which also means a higher per-block transaction volume, which could cause the block size limit to legitimately be hit much sooner than expected. Furthermore, due to difficulty adjustment being measured exclusively in blocks, the time until it adjusts to compensate would be prolonged. For example, if 50% of miners dropped off the network, blocks would be every 20 minutes on average and contain double the transactions they presently do. Even double would be approximately 850-900k, which potentially bumps up against the hard limit when empty blocks are taken into consideration. This situation would continue for a full month if no changes are made. If more miners drop off the network, most of this becomes linearly worse, but due to hitting the block size limit, the backlog would grow indefinitely until the adjustment occurs. To alleviate this risk, it seems reasonable to propose a hardfork to the difficulty adjustment algorithm so it can adapt quicker to such a significant drop in mining rate. BtcDrak tells me he has well-tested code for this in his altcoin, which has seen some roller-coaster hashrates, so it may even be possible to have such a proposal ready in time to be deployed alongside SegWit to take effect in time for the upcoming subsidy halving. If this slips, I think it may be reasonable to push for at least code-readiness before July, and possibly roll it into any other hardfork proposed before or around that time. I am unaware of any reason this would be controversial, so if anyone has a problem with such a change, please speak up sooner rather than later. Other ideas or concerns are of course welcome as well. Thanks, Luke