What you're describing is not an open AND decentralized (however way you want to define 'decentralized') platform, and its applications are much more limited.

What you're describing is not an open AND decentralized (however way you want to define 'decentralized') platform, and its applications are much more limited. And your scheme does require some amount of trust. Induction into the consensus node set would need to be controlled to prevent bad actors from disrupting the flow.