Moving to Gordon's world (a world I think the Theremini excels in), I have no doubt that he will do some amazing things with the instrument. The question is not "Can the things the theremini do be replaced by a host of other technologies?". With enough $ anything can. The real issue is, "What would you have to pay for all those technologies needed to replace your $300 Theremini and how much more time do you need to do that (time is $ of course)?"
Let's review some of the features/capabilities of the Theremini (centering on it here as a compositional tool):
1. Gestural Control both applied to line output and MIDI CV (Note, Pitch and Volume) to control other things. So you need to buy a theremin with CV control to start. You've just blown more than your $300 right there.
2. Ability to change to a wide variety sounds and edit them in many ways (and also change them on the fly through MIDI controlling wavetables and scan rates among other things). So you need a wavetable and substractive synth to control through CV from your theremin. They ain't cheap.
3. Built in speaker and Pitch display (at first I had doubts about the pitch display but as I play more it is a very viable substitute for pitch preview now that Moog fixed it to always display the correct pitch). And I don't have to have that darned buzzing going on in my ear. I really think Gordon will be able to make good use of that Pitch display.
4. Built in Digital Delay and real time control through MIDI.
5. Built in Filter control through app or real-time through MIDI
6. Ability to quantize - and control quantization amount in real time (I think this feature Gordon will really like as it can create some very interesting transitions and effects).
7. Ability to set a lot of scales for quantization modes - and control them in real time through MIDI (again this will allow for some really interesting harmonic transitions).
And I've left out a number of things related to volume, CC control, dynamic range adjustment, new Theremin mode, etc. - so I think you are likely talking $1000-2000 to replace all those Theremini functions (and the editor is free). We've just seen Thomas experimenting with filter format-like patches to get Talk Machine like sounds - add that in too.
And I assume (but have no control over or knowledge that) Moog is going to add other things that we all have been asking for down the road like ability to create your own wavetables and support for MIDI note output. $300 is really a pittance for all you get here from the composer's perspective.
Gordon completely stunned me with an inexpensive LostVolt Theremin and a couple pedals. I can't wait to hear what he is going to come up with throwing a Theremini in the mix.
Rich