The KDE developers working on this tablet initiative didn't decide on their own to come up with a more obscure name to fit other usually arcane open-source project names. Rather, there was a trademark issue concerning the Spark tablet name. As a result, they were forced to come up with a new name and they settled for the Vivaldi.
The Vivaldi tablet name was inspired by Antonio Vivaldi, an Italian Baroque music composer from the 1700s.
No other KDE tablet details or other announcements were shared today besides the name-change to Vivaldi. The Vivaldi name was announced via Aaron Seigo's blog.
You can read more of my thoughts on the KDE Vivaldi tablet when I was trying out the tablet hardware last month.