I don't think that is necessary. I could imagine a world where bitcoins are used for large portions of the economy, but the government still wants to use dollar

I don't think that is necessary. I could imagine a world where bitcoins are used for large portions of the economy, but the government still wants to use dollars. But there is no indication anything but online drug sales are actually being conducted in bitcoin. And even online drug dealers are looking for a replacement because bitcoin is an awful currency.