Well that's interesting. They're keeping people from using it as an LTI token on any ship. Haha. Sneaky.
You'll be able to buy your Anniversary Edition of the DUR tomorrow though. Standalone ship only though.
You can upgrade any ship into any other ship that is on sale and is of equal or greater value to your current ship.
IE: 50 Dollar x85 can become any ship that is valued at 50 or more. You can upgrade it as many times as you like, alwasy going up.