OK I've had some time to process this and finally get my head around it.
The successor to CeVIO Creative Studio, CeVIO AI will release in Q3 2020. That means it'll be out by the end of September. IA, ONE, Yuzuki Yukari and flower are all confirmed to be receiving vocals for it. It seems there will be physical versions. The vocals that are 100% confirmed are IA Talk, ONE Talk, Yuzuki Yukari and flower. IA English C and ONE Japanese will also likely be updated. There has been no official word on if IA Japanese will be released as a Song Voice for CeVIO AI. Techno-Speech said that they will make an announcement about currently existing vocals, since some will move to AI and others won't.
What I see as likely is this:
Song Voice:
IA (English + Japanese) / ONE (Japanese) / Yuzuki Yukari (Japanese) / flower (Japanese) / Sato Sasara (Japanese)
Talk Voice:
IA / ONE / Sato Sasara
Even though it makes me really sad, I don't know if the Color Voice Series will be moved over to CeVIO AI. Same goes for Takahashi and Suzuki Tsudumi, even if I'd really like to see it.
Regarding Yukari...
I'd like to make sure everyone is 100% aware that Yukari actually isn't owned entirely by AHS. She's primarily a VOCALOMARKETS character and vocal, and they can decide what they want to do with her. It seems that while AHS and TOKYO6 have moved to Synthesizer V, VOCALOMARKETS have chosen CeVIO. Also, it has been clarified by the head of VOCALOMARKETS that they don't intent to retire Yukari's VOCALOID4 vocal, and that this is simply a way of expanding the possibilities of Yukari. Jū Ayakura, who illustrated all of Yukari's previous designs, will return for her CeVIO AI vocal. I could see Akari receiving a vocal too if Yukari's is successful.
I think when it comes to English companies for now will focus on SynthV, but it'd be cool to see more English vocals for CeVIO too (give they're easier to use). I still love CeVIO a ton and I'm seriously excited for CeVIO AI!