Yup, there would be technical issues with a live performance, no doubt about that. Specifically interference between theremins, and the difficulty of the players in distinguishing one theremin from another.
With regards to interference - was the arrangement of the theremins in Lev's performance really as I have seen it in photographs, with them crowded into a tiny area, right next to each other? That was doomed from the start. I believe this was not such an issue at the Disney recreation - there was sufficient space between the players.
I am sure there are more ways to minimise interference than distance alone, such as assuring that the instruments do not share a common earth, and putting metal mesh walls between players. I also suspect that electronically synchronising the fixed oscillators of similar instruments would be of benefit, but that's just guesswork on my part.
I have been told, and was not surprised to learn, that players were having trouble distinguishing one instrument from another. Here I note that the Matryomin orchestra does not seem to experience this problem. Maybe it's as simple as headphones. I suspect that until someone tries that, we won't know for sure.
Outside of live performance, overdubbing would be the simplest way to create a recording. The piece does not strike me as relying so much on the dynamic interplay between performers found in more traditional musical forms.
