I really love vim keybindings and I use them wherever I can (firefox with vimperator, the shell etc), however I'm not sure that modes make sense on a window manager. In my opininon it doesn't have that many operations, and they don't differ that much from each other, I think that having to think which mode you're on and which one you need to use would only introduce friction and slow you down (in this case the normal mode is not that normal, i switch windows as often or more than I create new ones or switch layouts).

Another thing is that the operators, motions, and objects each need its modifier keys; in my opinion that just misses the point of having modes and one of the strong points of the vim keybindings. Because of that it was really hard for me to understand how to use Howm: the first time around I skipped the configuration part and went directly to the examples, and you don't mention anywhere there that q4c (for example) is really Alt_L+q, Alt_L+4, Alt_L+c. When I read the configuration part and the configuration file, to see each keybinding I got it, but still it took some googling to figure out that I needed to use xmodmap to know which keys are the MODXMASK.

EDIT: It seems you do mention that the operators, motions and objects need a modifier key, I missed it. Still, I think that it would be clearer if the keys to press were explicitly indicated (like Alt_L+q, Alt_L+4, Alt_L+c)