The Japanese language lends itself almost perfectly to Vocaloid, but yes, once the software gets more user friendly, and more English-language adaptable (and it will), like you said, no more divas. LOL!
When I first researched it, I was unsurprised to see that few singers will work with Vocaloid companies to do the samples...which are just vowel sounds.breaths etc.. They know what their future looks like.
6 figures to pay a diva or 4 to pay a good Vocalod programmer. Not hard math to follow. and when a ‘body’ is needed, hire a 3D animator for another 4 figures.
Done.