What you say is "completely wrong" is absolutely right. There are only 6 types of MSBs. No more, no less. They all have exact definitions in the eCFR. When registering as a MSB you must select one or more of the following six types. You can't select none, you can't write in a new type. All MSBs must be one these six.
(1) Currency dealer or exchanger.
(2) Check casher.
(3) Issuer of traveler's checks, money orders or stored value.
(4) Seller or redeemer of traveler's checks, money orders or stored value.
(5) Money transmitter.
(6) U.S. Postal Service.
The law doesn't allow any other type of MSB.
Oh really? Show me where in the BSA it defines "stored value" or "prepaid access". It's not there. These are just new categories of money transmitting businesses that FinCEN added to the regulations. In 2011, they removed "stored value" and added "prepaid access".
FinCEN can't write new law.
No, but they can write new regulations. However, they didn't, so they're not really following proper procedure by coming up with a new definition of "virtual currency" in a guidance document.