Grats!
I'm getting my first legendary this week. It's crazylate, but I guess I'll still be using it until pandas? It does kind of suck though that you can't transmog the legendaries.
They should make it so that you can transmog the old ones, as in from past expansions, but if it is relevant it shouldn't be eligible. That way, Sulfuras, Thunderfury, etc. all can be shown off, and the people who got the modern legendaries like Dragonwrath and Fangs would still feel like unique snowflakes.