It ain't broke, why fix it? Linear isn't broken. Just because people won't flag doesn't mean we should abandon linear. So far, that's the only valid reason I've been presented. Abandon linear so that people with more voting power (but not me) have even more to work with. I don't think we need it if people would just do their job.
And if people won't do their job, that's also no reason to push the work to bigger stakeholders. If they think their job is that worthless, then that should be reflected in the market, which will show how worthless Proof of Brain is on the open market (low STEEM price).
I don't think Proof of Brain is worthless. I think we can get our act together and do our jobs.
Phase 1. Good content: upvote. Bad content: flag.
Phase 2. ...
Phase 3: Profit.