Very interesting, very refreshing.

Curious: Why does the valve have a separate B/O wire? When or why does that B or O wire send a signal that is not identical to the corresponding W or Y wire? Why can’t the valve use the W or Y wire as its signal? Are there thermostats that do interesting things with these distinct O/B wires?

The W and Y terminals have their own function independent of the O signal. The Y signal energizes the contactor to power the compressor and outdoor fan motor. A Y signal without an O signal runs the unit in heating mode. A Y signal with an O signal energizes the reversing valve to initiate the cooling cycle. The W signal energizes the backup heat ( often electric strip heat).Hope that helps