The project works as it's currently designed, but I was turned on to a different sort of isolation solution by a Twitter follower (I'm sorry, but I don't remember who as I type  this). It's the SI8035AA-B-IU, which is a 3 channel logic level isolator. I believe internally the isolation barrier is crossed with RF transmission (which you could argue is induction) across an insulating barrier. The isolation drops form 5 kV to 1 kV, but that's still plenty for this application. The big difference is the cost. One of the SI chips is about $1.20 or so, and two of the optical chips (because each has 2 channels instead of 3) are just shy of $4. And, of course, you have to double those prices for each unit because there's a need for the same number of channels in each direction.