Additional points of interest which do not affect your actual argument, but which are good for clarification: the most responsive pipe organs use tracker action, which being mechanical allows much more control than the more "modern" but less responsive electropneumatic actions necessary for the very largest instruments. IT makes the action from pressing key to opening the pipe faster - much of the latency in the organ is often in the pneumatics - but of course cannot change the distance issues.
also Attack makes a huge difference to the sound on a well-voiced instrument, and this makes a huge difference. Subtleties in duration are of course also as vast on the Organ as they are with the piano and other instruments.
You don't even need to go as far as organs to see latency.
Low-pitched stringed instruments such as fretless/upright bass guitars have latency due to the mechanics of the strings themselves; e.g. jazz bass players have to account for this when playing. Most good jazz bass players do this unconsciously.
Polyphonic reed instruments (e.g. harmonicas, melodicas, accordions) all have this issue as well. Reeds of significant mass (i.e. lower-pitched reeds) can take tenths of a second to sound (more on older instruments).
Also: if you can feel the string in your fretting hand vibrate on a fretted instrument, you're doing it wrong. (The string does not vibrate past the fret -- that's the point of frets! If it does, you're not pressing firmly enough and you get fret buzz. Either that or your finger's on the wrong side of the fret and you're muting the sound.)
Generally the entire body of an acoustic guitar vibrates with the sound of a plucked string - the fretting hand (being the only hand currently attached to the guitar) would likely feel the vibration carrying from the body, through the neck of the guitar. It's faint, but nevertheless perceivable.
> The organ console is an electrical or pneumatic
> controller
I've no criticism of your theremin example though.
The classical pipe organ, often referred to as "the king of instruments", is a synthesiser. The organ console is an electrical or pneumatic controller, with no direct connection to the pipes. Most large organs have considerable "latency", due to the distance from the console to the pipe room. Some pipes may be as much as a hundred feet away from the player, so the sound will take over 90ms to reach them - several orders of magnitude more delay than a modern computer system.
The organ is still regarded as a highly expressive instrument, in spite of the relatively modest control a player has beyond simple pitch and duration. Although most organs have many stops which provide similar timbres to existing instruments, it is understood that the organ is an instrument in its own right and should be played as such, and is not merely a tool for emulating other instruments.
The idea that an electronic instrument should imitate acoustic instruments is simply a poverty of imagination. Electronic instruments, used in a manner that is sympathetic to their natural properties, can be absolutely as expressive as any acoustic instrument. The theremin has perhaps the worst user-interface of any musical instrument as the player has no physical contact with the instrument whatsoever, but is utterly beautiful when played by a master.
The challenge for electronic musicians is that they are often both performer and instrument-maker. A monosynth of any quality can be configured in a near-infinite variety of ways, many of which were completely unforeseen by the designer. Musicians working with modular systems or DSP programming environments have a blank canvas. We do not as yet have a good theoretical framework for this task, but electronic music is extremely young - no more than ninety years old at most. We are only just beginning to scratch the surface of what is possible.