I don't believe signing a petition would be necessary. I'm sure the folks at Moog Music are smart enough to tap into the internet resources to monitor the wants and needs of the theremin, synthesizer, and “effects using” musician’s communities.
I don't think it would be in our best interest to force the issue, and it wouldn't surprise me if they are occasionally annoyed by our collective whining. Such is human nature on both counts.
We should thank our lucky stars that Dr. Moog had a soft spot in his heart for the theremin and had almost single-handedly kept it alive long enough for us to enjoy what is perhaps its first real widespread popularity.
Moog Music, with or without Dr. Moog, is a business and as such must plan their designs and manufacturing to sustainable market conditions. While Moog has offered theremins of various quality levels for many years, they alone are not obligated to do so.
There is just not enough demand in the theremin market to sustain a company as its only product, especially a high-end, high priced theremin.
Both the Moog Ethervox and Etherwave Pro had a limited run and did not sell in large numbers mainly because of the high cost to manufacture and their high sell price, not that they weren’t highly desired. We can only hope they are working on a comparable design that would be available at a reasonably affordable price. (I don’t mean “cheap”. Quality goods always come at a “quality” price.)
The only other option is for someone, or some other company, to design, produce, and market their own quality theremins. However, they would also be limited by the same issues of low demand and high price. If that wasn’t the case, we’d already have one or more other companies doing so.