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).

Sha256^2 hashing is hardly used outside of cryptocurrency mining and unfortunately that's all those chips (by their very definition) are able to do.

You could still use it as conversation piece on your coffee table? Or as the world's slowest toaster?