Warpcache has introduced an origin shield for their multi-cdn solution. This feature, called Warpshield, protects origins against cache stampedes and reduces cost.
One of the challenges to solve in a multi-CDN setup is the amount of request that still reach the origin, for instance S3 or Google Cloud Storage. When combining multiple CDNs without internal origin shields in a multi-CDN setup, the amount of requests made to the origin is equal to the combined total amount of PoP in case your audience is global. This could easily be somewhere between 100 and 200 requests per file, depending on the CDNs. With the introduction this amount will be reduced to 1 single origin request per file for the duration of the TTL of the file.