I wrote a keyboard hook in C for Windows (I was using AHK but it was unreliable). Initially it was modal but I found over time that I would get caught out. So now it's not modal. I hold down capslock and then use ijkl to navigate etc. The only thing left that is modal is spacebar for select/visual mode but I still a have to hold down capslock for that (e.g. capslock down, space bar, ijkl to select text, capslock up). Also I was using hjkl but switched to ijkl to match the arrow keys. I don't use vim enough anymore to justify hjkl.

Holding down capslock turns out to not be a problem in practice. The main benefit of vim style navigation for me is not leaving the home row.