But why? I think it would be hard to argue that the mouse isn't significantly more efficient for, e.g. resize operations than the keyboard. And you have one right there on your desk, don't you? Don't you find it to be a waste that it can't make effective use of all your input devices even in situations where they could provide advantages?

Decade-long user of i3 here, I have three different keyboards (netbook to server) and three different trackpads\mouses -- the keyboard is more efficient for resize operations. I use focus-follows-mouse (agreed, why not use all devices) and fling the cursor all over the place all the time, but don't have to click and don't even have to use my fingers if I can drag my lower palm across the trackpad.

Yes i know that i3 has a lot of keyboard shortcuts, i'm saying what i'd expect it to also have in terms of mouse support - it isn't an either "this" or "that", it is both :-). One doesn't exclude the other.