my friend in Hong Kong is STILL waiting for a Cantonese Vocaloid. He's gonna be so salty when I tell him there's a new one and it's still Mandarin.
Phonetically, it's a different language, so Cantonese would be a similar amount of effort as adding French to Vocaloid
hate to break it to you but as far as we know, hai yi is on her own engine instead of vocaloid. this has the advantage of her possibly being cheaper, but also the disadvantage of her most likely being lower quality or hard to use.