A registration of speakers and reviews of them controlled by the WP foundation? Hmm no nothing could ever go wrong with that. Each speaker should enlist themselves for feedback and the feedback should be private to them I think. Any really bad ones the organizers would know about anyway since people often have easier time to complain about stuff than to praise it.
Also how many attempts does one get? One bad presentation, two bad presentations? And then bad according to who?

The whole idea I feel is partly whats bad with the community in some areas. That thinking should be cleared out in exchange for openness, embracing and free thinking and free speech. Not always the case in this community.