The whole purpose of blockchain is to support decentralised consensus. You don't need a blockchain if your currency is centralised and controlled by you.
We're getting dangerously close to centralized mining already. Why not run with that concept and try to make it work to your advantage with the full power of the US government behind you?
The fact that there are few major pools doesn't mean we're centralised. Key difference is anyone is free to mine, or start own pool, or switch to other pool (if you're mining).
Why run with concept of centralised, government cryptocurrency if we already have USD, what would be the difference?