One of its greatest virtues of Bitcoin is that the supply of Bitcoins is limited to 21 million
If the US treasury said that it was restructuring the USD such that there would be 21 million MegaDollars maximum, but that each of those MegaDollars could be dived up to infinity - just like Bitcion, does it suddenly become sound money?
OK. I see what you are saying. I modified your OP so as others can see what you are saying.
So the real question you are asking is: Does the fact that Bitcoin have a limit of 21 million make it sound money?
Now, everyone, debate away the very same economic debate that we have had from the start. Go!