I recently purchased an AIY Voice V1 from Micro Center. After reviewing the documentation, I saw no reason not to use a RPi 3 B+ with the kit. However, after much experimentation and research here and on the internet, I could not get the V1 kit to work with the 3 B+. A new version of the software became available a few days ago dated August 3. I thought that might solve the problem. Still no luck.
I scavenged an RPi 3 B from an earlier project and used that with the AIY Voice V1 instead. After installing the Aug 3 software package and performing an update, the AIY Voice V1 works as expected.
Bottom line: With the software currently available the AIY Voice V1 will only work with the RPi 3B, not the RPi 3B+