As an additional cool thing for being a legendary tier, what if the timer on your airdrops was cut in half? Small thing that could be really cool anyway.
Another Legendary Tier bonus: What if you could have your own custom glyph? I've been waiting for this forever. Let it cost plat, or even something for real money done through Warframe.com.
And now that we have so many advancements in the game, is there really no way to get umbra forma? If some way of getting them beyond Teshin and the occasional alert would be put into the game, that would be fantastic.