Create the world's most useless rainbow table? Crack passwords of whatever website still uses Sha256 to hash their passwords, and in an oddly specific turn of events uses double round at that? (disclaimer: I'm not sure if Bitcoin ASICs actually do double rounds on the hardware level, maybe you could use it for other obsolete insecure databases as well).
See they don't even do that. They don't complete the double sha and don't return the hash at the end, only nonces that meet targets. So they really are useless.Aw shucks. You just crushed my dream of creating a sha256 rainbow table ICO using repurposed mining hardware! I was just about to finish the whitepaper!
Seriously though, that's quite interesting. I always assumed that the ASICs were basically the sha256 algorithm cast in silicon, with most of the mining logic taking place on the software layer. Today I learned.