Even leaving aside the obvious supply and demand misunderstanding - unless everyone on Earth takes a spaceship to the asteroid to dig their own billion dollars worth of gold, the only way they will become fantasy billionaires is if government takes the gold from actual miners and redistributes it to them in return for their eternal political support.
“...takes the gold from actual miners...”
Maybe in another 500 years if we have a space colony around Jupiter or on Mars it MIGHT be feasible to mine this rock to supply the raw materials to building it.
The cost to get to the rock, mine it, and return back to earth (with a limited load) would be cost prohibitive. Perhaps could attach rockets to the rock and send it to earth?