Sorry, I've been away for a bit. The AFDS controller has a property already to activate the autoland. It would be better to put the listener on that property: /autopilot/autoland/engaged. Right now, that activates at 200 ft agl, but that is easily changed to 150 ft (see AFDS.nas, line 396).
For the mach with pitch, I haven't had a chance to do any further testing, but the main problem I noticed was on switching from IAS to Mach mode and then adjusting the mach. The pitch didn't drop below 0, but the VS did. In general, the speed should change fairly gradually in response to changes to the commanded speed (or mach). It shouldn't pitch down too much. We're in a passenger liner, not a military jet.
I'm a little skeptical (without having tried it) about scaling the mach up by x1000. The IAS values we're dealing with are in the range of 200-300 (approx), so 865 is pretty far above that and the PID controller is likely to react differently to that high a value.