Mogu Rune of Fate
You have better than one in three odds to get no loot in six coins. Hardly unbelievable.
Anyway, your system would be laughably easy to game to win specific gear drops, which is something Blizzard has expressed no interest in allowing. Ghostcrawler has said that it is unfortunate for some people to be chronically unlucky (you're not anywhere close to that yet, btw), but they're going to have to come up with a much cleaner system than what you're suggesting if they want it to work right.
It would make much more sense to enable an algorithm to increase your chance to win after each unsuccessful attempt. Maybe I am expecting too much. I'll keep my fingers crossed for some kind of positive change in patch 5.3.
I just recently got a dagger from Dark Animus from a coin, first piece of coin gear I got since ToT was released, pretty much using my coins every week.
And you know what? I'm happy for the extra chance for gear. It does suck to get on a unlucky streak (which I think 5.3 is doing something about, dunno if it effects normal coin rolls too), but its nice to get another shot at it if a boss is being stubborn and won't drop it.
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