I think your hesitation about sharing may be linked to the fact that sharing the brainstorm feels like it's real-time, so to share with your coworkers would involve breaking their flow and dragging them into your current brainstorm. That explanation seems to fit with you not wanting to change the mood - am I correct in this assumption?
I'm really glad you liked your nudges - we were initially not sure people would "get" them. We're a little worried about async brainstorming, because a lot of the real value from brainstorming comes from stealing your coworkers' ideas and building on them - so you make their ideas better. Async makes this more difficult.
I love your idea about email being the conduit. I think i'd like to build on that :), and that with tools like mailgun, it's not going to be terribly hard. Thanks a lot for this 3rd paragraph - a lot of actionable ideas here.
Thanks for your support - we hope to make it into something awesome too :).