Fascinating, I have never had it dropped. And I've already seen hundreds of legendaries (usually around 5-6 each day). Not once Immortal chest. Don't take it as a rant, other legendaries are good too, it's just that RNG is fascinating.
I'm a magnet for gloves, 2H weapons and Fire Walkers.
I have all possible 2H weapons drop on me several times, skorns, warmongers, grand vizier, etc...
Gloves are always either frostburn or gladiator, either brimstone material.
I have a collection of Fire Walkers already one with good Int other with good Str/Dex but none with all res which is what make them worth something, I'm always praying for some Ice Climbers with movement speed when I see "Boots" legendary but never had the luck.
Lately I've also had quite a few lvl 58 legs, like wizard hat Dark Mage's Shade which can't even been turned into brimstones...
Never had an IK drop, lucky drops so far were a couple of average Natalya's embrace which got me 60M on AH and a good Dead Man Legacy which also got me 60M, others have always been worth less than 5M
Neither me nor my friends have ever seen an Echoing Fury drop. That is in an accumulated play time of way more than 1000+ hours. We start to believe EF's don't drop, they're just cheated items that some people bought on the AH :-P
I had a "lucky" streak of 8 legendary glove drops in 2 days though. 3 Gladiator's, 5 Forstburn's. [Insert random RNG flame here]
Wow, that is... quite a comprehensive list. Do you keep track of your legendaries? Like, do you take screenshots every time or scan them or something like that? Or is it just based on your memories? I've got way less than 1000 hours play time and I can't tell for sure how often I've found some of the less interesting legendaries...