The discussion[1] over "maximise" leaned towards "that's dumb, only dumb people want that" for a very long time, and it's still the one thing in i3 I find jarring.
To maximise a window temporarily but keep your status bar or avoid your program going into "full screen mode" and hiding UI from you, you have to move it to some empty desktop and just deal with the fact that when you put it back on the original desktop it might not end up where it came from.