What is there that could possibly be interesting about this letter?

I is so devoid of character, that you have to throw some serifs on it in particular sans typefaces just for legibility. It’s the only letter that does this.

But I is significant as a building block. Remember my rant against wild gs? If you want a wild typeface, make a wild I!

The reason is because the vertical stroke of I immediately echoes through a type system in a pretty gnarly way.

Lowercase i appears humble as well, but functions as a building block just like its capital counterpart.

In monospace typefaces (where each glyph occupies the same horizontal space), i has to really stretch out to fill the space.

This is even more dramatic in italics, where there are no serifs, only entry and exit strokes. ✌