Afaik this is not possible, but what you can definitely do is display a message of your liking in the statusbar by entering the 'system mode' and then trigger certain actions by predefined keys. Those you can assign with a simple script like THIS
In your ~.i3/config you can use somehting like:
# Set shut down, restart and locking features
bindsym $mod+0 mode "$mode_system"
set $mode_system (l)ock, (e)xit, switch_(u)ser, (s)uspend, (h)ibernate, (r)eboot, (Shift+s)hutdown
mode "$mode_system" {
bindsym l exec --no-startup-id i3exit lock, mode "default"
bindsym s exec --no-startup-id i3exit suspend, mode "default"
bindsym u exec --no-startup-id i3exit switch_user, mode "default"
bindsym e exec --no-startup-id i3exit logout, mode "default"
bindsym h exec --no-startup-id i3exit hibernate, mode "default"
bindsym r exec --no-startup-id i3exit reboot, mode "default"
bindsym Shift+s exec --no-startup-id i3exit shutdown, mode "default"
# exit system mode: "Enter" or "Escape"
bindsym Return mode "default"
bindsym Escape mode "default"
}