I'm sur[prised that this hasn't gained more traction. Currently there is no way to have private group conversations within Flowdock, which means using additional software, such as email or Hangouts.
After having trialled Glip, this was a well-used feature by my team. We found some groups used quite regularly, based around interests and skill base.
Pinning messages and inbox items is discussed in this suggestion:
I'd suggest focussing discussion and votes in that thread.
Yes, polls are very useful for community discussions.
This would be very helpful, though I think that it would be better on Messages rather than Inbox items.