Workspaces:
 - Workspaces are tied to monitors and there's no way to move a workspace
   to a different monitor
 - Can't use mod+shift+arrow to move a window from one monitor to another
 - No way to set predefined workspaces. I always want the left monitor
   to have workspaces 1-5, right monitor workspaces 6-10.

Sizing:
 - No option to show window dimensions while resizing. Other WMs show a
   pop-up. Having a pop-up would also solve the "forgot I was in resize
   mode" problem.
 - Can't resize terminals based on columns/rows. Other WMs snap to columns
   and rows when resizing. I want to be able to "grow by one character"
   rather than "grow by n pixels" or "grow by x% of the screen"
 - No way to set a predefined screen layout. I want to be able to optimize
   to have as many terminals be 80 columns as possible, or have one pane
   that is always 640 pixels wide.

IPC
 - There's a nice JSON-based IPC interface for getting the current state
   but changing state requires crafting text commands.

Configuration:
 - Things like this: 
      bindsym $mod+2 workspace 2
      bindsym $mod+Shift+at move workspace 2
   Why not:
      bindsym $mod+Shift+2 move workspace 2
   Using 'at' makes the behavior depend on keyboard layout, and who can
   remember all the X symbol names anyway?
 - The default settings for the i3bar are stupid. "DHCP: yes", "VPN: no",
   "No battery". In what scenario do I ever want to know my IPv6 address
   in a form that I can't copy and paste?

Other:
 - No compositing, and flicker when switching workspaces!
 - Shouldn't there be a Quake-style pulldown console for typing those
   i3 commands?