This all started when I thought it would be cool to run my acoustic through my pedalboard as an effects sidechain - add some verb, delays, loops, etc. without duplicating effects I already have on my electric rig. I still don't know if this is actually useful.
Even if it's not, this at least allows me to use a single tuner on my rig for both guitars, rather than replugging stuff when I switch off or what have you.
Further, I need to fit this, a tuner, an EQ, and DI on a micro pedalboard that fits inside my acoustic guitar case, so it's got to be compact. Hence the combined A/B and output splitter. It's completely passive and unbuffered (aside from my acoustic pre-amp), so we'll see how it works.
I can get away with not having A/B/Y function (A or B or both) on the output because I'm using the tuner as a mute on the DI output. Technically I don't need the switchable Y output since I can mute the electric side with the volume pedal, but I didn't think of that and having this option seems safer and more flexible.