Following up on this. The scaffolding for this (BaseExecutor.get_health() hook, scheduler-side polling, the new /monitor/health entry) is up as a draft PR: https://github.com/apache/airflow/pull/76410. It doesn't change behavior for any existing executor yet, nothing implements the hook in this PR.
If there are no objections by Monday, November 10, I'll take that as consensus and move ahead with a concrete CeleryExecutor implementation on top of this, per the plan in the original post. Thanks again for the input so far.
