Surely, the altimeter and rad alt are a clear indicator of Ground to Air mode, and vica versa??
And whats all this twaddle about LGCIUs? Confusion reigns supreme. What has cargo door indication got to do with air/gnd sensing? I think you've confused the many functions of the LGCIU. At it's basic level, it gives you L/G indication, and controls it up/down. Additionally, it tells the FACs, FWC, SECs and all the other systems the state of the aircraft, so the flight envelope is modified accordingly. Everything from the CIDS, Radar, Door indication, nearly everything passes through those boxes. Only one LGCIU is in command for a sector, they swap over at each retraction selection, if that's what you mean by alternate operation. Actual air/gnd sensing is done by a combination of N,L,R oleo extensions and compressions only. It's a more sophisticated PSEU from the 767.
Truck tilt on the 777 is more to do with allowing it to be retracted into the u/c bay. Similar to the 340 where the leg has to be compressed.
Wheel speed is used for autobrake, antiskid, autospoilers and thrust reverse on some types. It depends on who makes it. Or it's a combination for backup and improved performance. An indication for Air/gnd transition would seem pretty pointless since you would have felt the bump. Going the other way, the brakes have to be applied to stop the wheels spinning, so oleo extension is the logical method by which this is achieved, wheel speed wouldn't be much use for air/gnd sensing would it?