> This may be hard to realise with lots of devices and wireless connections.
Assuming that the latency of the wireless connections is at least relatively predictable, you could just introduce a suitable delay like with NTP time syncing, right? Of course, it's possible that the latency will be wildly unpredictable and in that case it's pretty much impossible, but that doesn't have to be the case.
In the parent's case this latency includes time from a human key press (piano key). The other cases you mention can be compensated for but of course the human input is non-predictable.
Assuming that the latency of the wireless connections is at least relatively predictable, you could just introduce a suitable delay like with NTP time syncing, right? Of course, it's possible that the latency will be wildly unpredictable and in that case it's pretty much impossible, but that doesn't have to be the case.