You only have to hit the notes at the right time and the instrument plays itself JS Bach
How does the virtual pipe organ fit in this rich history of bellows and pallets?
It's certainly a new, and emerging, topic. There seems to be no official definition as yet, not even a Wikipedia page at the time of writing.
Perhaps it is any organ that wants to sound like it has pipes? For example electronic organs, since the 1930s or so, have been getting progressively better at this. And others have been taking the sound in other wonderful directions too.
In the computing world, virtual tends to mean an emulation of some kind. Maybe of reality, or even another computer. But something that has been simulated, as opposed to being built from moving parts. Bits, bytes and pixels, rather than wood, metal and string.
Soon after electronics got good enough to build an organ, they got good enough to build the universal machine that Turing described. This is a properly versatile invention, and still showing us its abilities. Perhaps though this leads to an expectation, because the computer can do so many things, it is always the best tool for the job.
There could be a case for some division of labour here. Especially in the musical world, simpler is often better, and more playable too. If you have a keyboard or synth that can create a refined sound, and a computer that's good at crunching numbers, why not take advantage of both of these strengths?