That is how it currently is.
In Shadowlands Legendary items are transmoggable via normal rules, therefor everyone who can equip it and has it should be able to use it.
I am confident if a Rogue and Warrior goes to the PTR and has it they can tmog it.
If not then I expect riots when SL goes live. It is a kick in the teeth to the classes that originally used the damned things.