Maybe there's an oil deposit underneath your house?
Hm. That very much reminds me of the movie There Will Be Blood. And the farmers got suckered and sold their land.
Anyway, Blackrock? They own everything. Just go to Yahoo Finance or any other site that lists the major shareholders of any corporation that's public and 99 times out of 100 they're one of the top 3 holders of any given stock. It's crazy. In fact, the same names pop up every time, like Vanguard Group, State Street Corporation, etc. Anyway.
The question OP posed is silly IMO. It's a scenario that isn't going to happen, and it's not even an interesting hypothetical. Unless Blackrock had some inside information along the lines of the US government intending to make an enormous purchase of bitcoin, they would have no more information about bitcoin's future performance than any of us. Oil can be located underneath a house without the homeowners knowing it, but bitcoin? Nah.
I mean when you are as rich as having trillions of dollars trusted to you to do something, it's normal that you are going to be able to purchase everything. Think about it this way, if they wanted to use all of their money to buy bitcoin at this price, which they can't, if they try to buy a lot, the price would go up, but if they wanted to buy everything at this price, they could buy the entire crypto space like 5 times over, they are THAT big.
This is why it doesn't really matter what we want to do or what we are going to do, it's important that we just let it happen and hope that their entry would make it super high. Instead of being worried about them, we should consider being hyped about them getitng involved. This could be done by thinking how much money you can make, I mean if you buy as much as you can right now, that means you are going to end up with a ton of money later on, when blackrock joins with their ETF, you literally have a recipe to get richer.