Proof-of-work cryptocurrencies moved toward complex hash functions that are "ASIC resistant" in order to attempt to keep mining power as distributed as possible (for CPUs), because whatever highly-funded manufacturer designs the most-optimized and fastest ASICs gains concentrated mining power. ASIC hash/W efficiency doubles every couple of years, so using them as heaters becomes cost-ineffective as difficulty adjusts.

But what if we turned this all on its head and intentionally designed a hash function that is "ASIC optimized" so that the perfect ASIC miner design could be found quickly (perhaps at its very conception), and miners became a generic commodity item, "grey goo miners", and used them as space heaters in cold climates, or maybe even wherever electric heating was needed in industry? That way mining would be as distributed as the need for electric heating, and its energy would be put to good use. It might also put a ceiling on the total electricity consumed because it would be hard to compete with any miner whose electric bills are "free" (relatively).