I agree that a logo should get updated once in a while, but I don't think designing a 'future proof' logo is possible. Your options look nice, but I don't like that they don't have these serifs or how to call them on the letter B at the top and at the bottom. You cannot change the basics, Bitcoin symbol without serifs is very unlikely to become widely recognized and accepted. I believe that logos tend to preserve the basis even when they do change. And to be honest, I'm not sure Bitcoin needs a cool logo because it's not a company. The $ symbol doesn't change with time, and perhaps neither should BTC.