Color me backward and verbose, but I do not see how you can have a serious discussion of a complex book like The Blind Assassin in 140-character bites from zillions of people. Can someone explain to me how this will be possible?
“Global, participatory”? More like “fragmented, spotty, chaotic, random, hit-or-miss, superficial” dontcha think?
That’s Atwood in a nutshell! 
How many characters are in your post?
I participate in an online bookclub based in a chatroom. Each message posted only needs to be a sentence long to make a point during an interactive discussion.
But a chatroom has a limited participation, right? It’s hardly global. I know that when I send a text message, I have to spend some time editing to make it fit.
You can limit (apparent) participation by creating a list of the more interesting participants and using that to follow the discussion rather than the hash tag. I don’t think the 140 character limit is an issue - just continue your thought in the next tweet. It may well turn out to be a chaotic mess, but there’s no harm or real cost in trying such an experiment.