Isolated remote logic signal w/ opto-something?

[PRR]

> the controller & effect states will get out of sync,

At a very dummy level: one pulse means off, two pulses in 1/10 second means on. More complexity, and some delay (which could be reduced), but not-knowing the current state you can also move to a known state.

But as R.G. says, CPUs are cheap as chips now, and you could bleep a MIDI-like byte command specifying device, note, loudness, whatever (diode on/off, tone hi/low, etc). Since the device can be part of the command the control cable can be daisy-chained instead of octopus.

[R.G.]

Just sayin'     

MIDI is remarkably like async (some early MIDI send/receivers were mildly modded async cards) and many very low end uCs have async hardware built in. It only needs the physical layer, if any.

If you have a glimmer that you're going to do anything bigger than off/on, that's another vote for making it programmable.

One of the engineer's mantras is if you can't make it work forever, at least make it easy to fix.

[Rob Strand]

MIDI is remarkably like async (some early MIDI send/receivers were mildly modded async cards) and many very low end uCs have async hardware built in. It only needs the physical layer, if any.

One point is daisy chaining using MIDI THRU connections are one way.  If you get an error there's no way to request a resend.