Only yesterday I thought about proposing this idea. I used to think using "i" or "j" was a type of local feature, like using a comma or a period as a decimal separator, or different writing for less-or-equal, but it looks like even in the English-speaking world mathematics use "i", and "j" is only used by electric engineers.

Possible argument against the "i" suffix is that its capital form "I" can be confused with the "l" suffix for longs (but it is no longer applicable in Python 3) and digit "1". Although there is more similarity between "l" and "1" them between them both and "I", and there are other pairs of potentially confusing characters: "O" (for octals) and "0", "B" (for binaries) and "8".