I don't think that the US will make Bitcoin or at least other currency to replace their dollar. It's a radical change and it won't simply happen. US, despite who will be the sitting President and what party he/she is, they won't abide by that. Good thing if they will support Bitcoin but so far that is not the case.
Blackrock is a huge financial entity, trillions worth, but I also doubt that they will let crypto takes over. For them it's business as usual, if they can make money out of it and continue to dominate the world order then they will jump on the hype and that's what they are doing right now.
I mean think about it, if you are a rich company like them, and you are making a lot of money, does it really matter to you if it is in dollars or in anything else? They do not really care and they will end up with as much profit as they would like to and they will continue that way for a long time.
I get that it is not going to be that easy, and I know that it is going to take a while, but they are not doing business just in the USA anyway, they are dealing with foreign companies as well, so they are used to earning money in different currency forms, in this case it is not euro, it is not yuan, but it is bitcoin and they must be fine about it. Think about it we are talking about as much profit as we can for them so they are probably quite happy.