Well, humans have carbon based brains and up to this point Cylons have silica based ones. If they found a way to use a different base material, then that begs the question of "what is a human"? The premise has always been that the Cylons were created by man, they evolved and then rebelled. Funny thing is that they evolved into beings that look like the ones they want to destroy. The ultimate irony would be that they eventually hit upon technology to actually create a human "in their own likeness". They then evolve into the very thing they both hated and envied: fully human. They'd need a lot of therapy to sort all that out.