We've had Yamaha Vocaloid for over two decades now, and Synthesizer V is probably coming up on a decade too now. They're like any other synth: MIDI (plus phonemes) in, sound out. It's a tool of musical expression, like any other instrument.

Hatsune Miku (Fujita Saki) is arguably the most prolific singer in the world, if you consider every Vocaloid user and the millions of songs that have come out of it.

So I don't think there's any uncharted territory...we still have singers, and sampled VST instruments didn't stop instrumentalists from existing; if anything, most of these newcomer generative AI tools are far less flexible or creatively useful than the vast array of synthesis tools musicians already use.