Sors, I like your idea. Each language gets voicebank names in their own language, which I imagine makes things a lot more straightforward and understandable to the native users of each language. Have you looked up common kanji suffixes from existing Japanese banks?
Hmm... for sunetoha I've got it all planned out, so it's just called neutral, soft, and power. I don't have any particular theme in mind because it's a character-less UTAU. As for Dominic, there's less planning involved, so I might end up choosing names that are more reflective of his character and story. For example, I've got an experimental bank with edited samples, and I want to think of a name that suggests that he magically trapped himself inside of a cell phone, or something.
And then with the seibetsus, almost all of them have a duality theme, so they won't be getting banks outside of their two mains. It's some weird names I came up with years ago that don't make much sense.