This growth, if it continues, threatens to outpace the current mechanism designed to maintain a steady block time of approximately 10 minutes. The crux of the issue lies in the finite limit of leading zeros that can be accommodated in the target value for a valid block hash, a constraint dictated by the 256-bit (64 hexadecimal digits) structure of the target value. Currently, with around 19-20 leading zeros already in place, the system is left with a margin of roughly 44-45 zeros before reaching its upper limit. The concern is that double exponential growth in hash rate could expedite the arrival at this threshold far sooner than linear projections might suggest, potentially destabilizing block times and by extension, network stability within the next decade.

Several questions were posed to the mailing list community, seeking insights into whether formal analyses exist that corroborate the likelihood of such accelerated growth patterns in Bitcoin's hash rate, alongside inquiries into viable long-term solutions and the trade-offs they present. Among the suggested approaches to mitigate these challenges are the possibilities of adjusting the difficulty more frequently, altering the difficulty adjustment algorithm itself, or even changing the proof-of-work algorithm entirely.

In response to these concerns, a novel solution was proposed to avoid necessitating a hard fork while addressing the impending limitations of the current difficulty adjustment mechanism. The suggestion involves maintaining miners on the SHA256 algorithm but introducing a requirement for a secondary hashing to achieve a new difficulty target. This would entail miners publishing blocks when two conditions are met: first, when the SHA256 hash of the block header equals 1, and second, when the double SHA256 hash of the same header is less than a newly introduced secondary target. This secondary target would dynamically adjust based on the primary target, ensuring blocks are verified through both the initial and secondary difficulty assessments. This approach aims to sustain network stability by adapting the verification process to accommodate growing computational power without the need for significant structural changes to the existing framework.