Hey, I like the idea of this thread! Kazehiki has an English voicebank that's very whispery, if you don't mind his accent.
Akihana has two English voicebanks, one being a soft append...Not sure if that's exactly what you're looking for, but it's a start!
Kurobousuku's English is decently soft as well.
I'm not really looking for any UTAUs at the moment, but I would love a young female arpasing voice and/or an understandable high-quality CV.