uhh, why? are people mispronouncing them so that they sound the same? I guess they share a recent-ish etymological ancestor anyway, so it probably wouldn't be too much of a loss: I did not even know iniquity was an English word, FWIW :-) thanks for sharing
They're too close in pronounciation and spelling, so I just doubt they can both survive as distinct words in regular usage -- and "inequity" is now far more commonly used than "iniquity".
You're welcome for the word, short-lived as it may be from this point on! :-)