This is a purely educational question and not a request for protocol expansion.
Here in Switzerland there’s a company, myStrom, that makes smart home devices with very simple web APIs built in. For their buttons they use extremely primitive web hooks to deliver the events: https://mystrom.ch/wp-content/uploads/REST_API_WBS-1.txt
This got me thinking, that there may be devices that can’t keep a websocket connection, or possibly multiple websocket connections opened and implementing web hooks would be much simpler for them. It’d allow the device to hibernate in between samples, for example.
The w3c has recently standardized a protocol to establish web hook subscriptions: https://www.w3.org/TR/websub/
Would it make sense to allow things to provide web hooks instead of a socket for updates?