I'm happy with how it looks now. Logic high is not +5V -- it only really has to clear a bit beyond +3V for that, which it is doing.

The timing is now very similar to how the factory kernels do it, except Hijack now allows one extra microsecond for logic 0->1 rise time on SDA before clocking the bit out.

So, very safe for stock hardware.
How's the fan controller dealing with it now?

Cheers