I'm with you on setting up a bug/issue tracker for us and with the flow you posted.
Brainstorming imho is just a one time event to get us started and should stay in the worksheet. It would only clutter up an issue tracker. We probably should not add comments there, but after everyone is finished with entering his stuff, discuss things that seem important right here.
How about a moderated forum on nxtcrypto so we can create individual threads for the brainstorming idea discussion and lock them when done? We can post weekly summaries back here.
Between the 1 Thread to Rule Them All, the trolls, and the drama, doing active work on this thread will create additional challenges.
I'd say keep it simple and not spend too much time with committee self-organization. As long as we don't have problems here, let's stay here. We can always arrange something else later in case we see the need.
Nevertheless, some kind of issue tracker would be good to have a common way of documenting projects, ideas, bounties, etc..