As threatened in this thread, I have programmed an Altura Theremin effect for Reaper users. It is in the Jesusonic (JS) effects series and can be downloaded at:
https://stash.reaper.fm/v/41257/altura_xy
Near and Far Octaves are set differently in the effect. The near octave is set using a ‘Near Octave’ control, but the far octave is set using a near-octave multiplier.
The key is set using the effect’s Key selection. It provides the same range as the Altura Key control.
The set-up instructions to connect the Altura to the effect CC controllers is shown in the file, itself.
To install the effect, go to the ‘Options/Show REAPER resource path in explorer/finder’ menu. (It works just as well in the Linux version of Reaper.) Then open the Effects folder and save the file there. The effect will be available when you next choose ‘Add’ in the Effects panel.
It’s not perfect, but then, I’m not perfect! I think it is the best that can be achieved with the Jesusonic language and platform. I think the new feature request will provide the best solution.