The third scenario is the one you presented in your first post, the fourth is going back to gold and silver and while you believe more in this scenario what it is going to happen when we get access to the technology to explore the space and get as much silver and gold as we want?
I don't think we are anywhere near the level of development where one can really consider strip mining asteroids, etc. By the time that's viable, it would probably be a post-scarcity economy anyway.
There is also the chemical creation of gold. Alchemy has succeeded in the modern age! But this requires radioactive reactions that are currently too expensive. This effectively puts an upper bound on the price of gold.