I have a couple of ideas, at least on interface/user interaction.
How about if the first thing you type into the input field is a space, switch to auto-complete mode instead of the default search mode. You'd need an indicator to show what mode you're in I suppose, and subsequent hits on the spacebar in the first column of the field would toggle modes. I have no idea how you'd go about doing the actual autocomplete part, but that's why you're the coder, right?
Another method would be to have 2 fields instead of one. The second would be the equivalent of the Run dialog, and would only require you to hit tab to swtich from primary to secondary fields... I don't like this idea as much as the first one, since it would mean you'd need to tab twice to get to the search list.
Hmmm. What if, when you hold down the activation hotkey it starts up in the alternate mode. Same keys involved, just a change in behavior when held vs tapped. Double tapping the hot-key is another option. Or maybe rather than closing/hiding FARR on a second tap of the hotkey, swith to auto-complete mode. You would still have the Esc key as a means of closing the window.
Ok, enough ideas for one day. Feel free to use any, all, or none of them.
Hmm. I just found something interesting -- if I hold Alt+' (my custom trigger hotkey for FARR), then not only does the FARR window flicker in and out, it slowly shrinks from the right, one pixel at a time. Wierd.