We are in the midst of the Vocaloid 3 generation and the 4th isn't going to be that far away. The question is : What do you want to see be made into the software? (Besides Backwards compatability)
My answer? Well :
- Speech to come as a default function. There's a reason it's VOCALoid and not SINGloid, previously the only way a Vocaloid can talk is through V-flex, which was only combatable for Ryuto. There was also something being made for GUMI in V3 but I don't know much about that. But no if a Vocaloid can sing then surely they could speak.
- Change the tone of voice. This is actually something that can be done in Voiceroid although it's apparently not that great. Even so it'd be nice to see it without any need to change the voicebank (Append/Extends currently serve as the different tones of voice, not too great when you want an in-between tone without editing outside the software)
- Multi-lingual banks. I'm aware that this one is going to be hard and would barely even make it in the 4th gen due to potential glitches in the voice. However I would deem this as the ultimate voicebank as it would have a very large range of phenomes for the user to play around with and even potentially reach new languages than what we already have. Even if it didn't have all phenomes for all languages even just a mixture of English and Japanese phenomes would be a great.