Thanks for the bumps, y'all! The additional context is super helpful.
For anybody running an on-prem deployment, we recently defined an environment variable that is capable of enabling this. By setting WORKFLOWS_WEBHOOKS_INCLUDE_RAW_PAYLOAD to true, you can access the raw request body as startTrigger.metadata.rawDataBase64. This should be available on the 3.196 release.
Note that this functionality does not currently exist for cloud instances, as we are evaluating the potential impact on our infrastructure, but I'll provide another update as soon as I can. 