In my opinion, the subsection "webhook vs websocket" could be moved to the Subscribing and Unsubscribing section.

Existing Wording:

webhook vs websocket

A subsciber specifies the preferred hub.channel.type of either webhook or websocket during creation of its subscription. Only the event notification and subscription denied exchanges are affected by the channel type. Subscribers SHOULD use websockets when they are unable to host an accessible callback url.
Implementer feedback is solicited around the preference and desired optionality of webhooks and websockets.