That makes for some genuinely interesting thought experiments.
What if, this actually becomes possible, but we discover that because we previously couldn't hear these frequencies, our instruments and equipment are HORRIBLY mis-tuned and sound terrible? We may end up having to re-record tons of stuff.
Something something premature optimization. And part of me is glad that the art of hand-making instruments is not yet lost; we might need the originals in the future.
Disclaimer: I say this as a completely naive person when it comes to instruments. The answer to this may be "if it wasn't built to resonate at frequency X, it won't by itself," which would be a good thing.
Most instruments generate harmonics that are integer multiples of the fundamental frequency, and some go a lot higher than human hearing. As you go up the harmonic series, the harmonics get (logarithmically) closer together. Our brains interpret close-together notes as dissonant, so higher harmonics could be kind of obnoxious to hear together. They might be "in-tune", but just too close to be enjoyable. (Imagine an extremely bright harpsichord.)
There's another effect that comes into play, though. There's a minimum pitch separation between simultaneous notes that we expect, and when notes are closer than that, they clash. That separation is usually around a minor third (~300 cents) in most of the human hearing range, but in the bass it's a lot wider, and in the high treble it's smaller. That's why you can play two notes a major second apart (~200 cents) on a piano in the high treble and it sounds okay, but down in the low bass it sounds muddy if they're closer than about a major third or perfect fourth (~400-500 cents). So, if we extrapolate into higher frequency ranges, then it's not unreasonable to expect that we would be able to interpret musical intervals that are a lot closer than 200 cents as consonant.
It's also possible that the minimum note separation thing is just an artifact of how our ears physically work, and that an artificial ear would have no such limitation. Which could open the possibility of enjoying kinds of music that we can't currently imagine as pleasant with our normal ears.
Because of the power decrease as you go up the overtone series, I'd suspect that being able to hear higher frequencies wouldn't cause very much trouble. However, the ability to hear higher fundamental frequencies would surely change harmonic theory! This is assuming that our pitch perception of high fundamental frequencies increased accordingly.
Even if the engineer pressed the "192" button on their field recorder or DAW, chances are the instrument isn't going to be doing much interesting over 20kHz and/or the microphone isn't going to be particularly sensitive over 20kHz.
My webapp manages photos for photography competitions. People upload 30MB JPEGs that would be visually lossless at a tenth of that file size. And I keep the originals, but actually resize down to 300KB for every function within the software. Haven't had a single complaint about image quality... :)
What if, this actually becomes possible, but we discover that because we previously couldn't hear these frequencies, our instruments and equipment are HORRIBLY mis-tuned and sound terrible? We may end up having to re-record tons of stuff.
Something something premature optimization. And part of me is glad that the art of hand-making instruments is not yet lost; we might need the originals in the future.
Disclaimer: I say this as a completely naive person when it comes to instruments. The answer to this may be "if it wasn't built to resonate at frequency X, it won't by itself," which would be a good thing.