Given the limited feedback so far I don't think we should consider the soft upgrade option. I would prefer first release with istat defaulted off, but would not vote -1 if community thinks it is better with it defaulted on.
I also wanted to say that I do think the istat feature is a good one, and what I am most concerned about is not bugs in istat. I am worried about application impact of istat doing what it is designed to do, run work in background. I just don't have a good feel whether defaulting it on will cause problems in existing applications. Also once we release with it defaulted on, I think it is harder to change this in the future. If apache supported betas, it would be great to release this defaulted on.
