Kron Tech posted something a couple years ago about export controls limiting how high they can go with the frame rates. However from what I can find for Canada and the US only cameras capable of more than 225,000 fps are export controlled, and in the EU it appears to be over 1,000,000 fps.
The issue is that to get higher frame rates (with the 1.4 at least), a feature needs to be added to allow smaller vertical frame sizes than 96 pixels. By doing so, they may open the door to frame rates over the magic number. I suspect implementing a hard limit once that feature is added is tricky, but I could be wrong.
I could also see, and this is pure conjecture on my part, the US or Canadian government deciding that once that feature is added the camera would be "capable of being easily re-programmed" to achieve higher frame rates than 225,000. That could be a legal can of worms Kron Tech doesn't want to open as the US export market is probably vital to them.
I hope I'm wrong as I've also been patiently waiting for higher frame rates on my 1.4!
G