long time lurker; not much of a poster...
Nice work!
Unlike mining, this challenge won't get harder. If 1 BTC = 1,000,000 USD, which address will be cracked up to?
Without a clear pattern it will be quite hard to get far. It is basically like generating addresses with a certain entropy to them.
I doubt we will get much further than the 50 range without additional info or significant calculating power.