"Typically an STC which covers an external payload mount won't list the specific item"
In respect to camera mounts there appears to no requirement for the payload itself to be approved. In UK, Pre EASA you needed a Proof of Design and Performance for the payload. This was meant to prove the payload could cope with the rigours of flying and wouldn't fall apart. I wrote one myself for a particular gimbal
But now there is apparently/could be wrong/grey area
no requirement from EASA for the payloads dangling from hard points to be "certified". However the payloads do need to conform to whatever the STC of the mount or bracket stipulates. If the mount details a model number then you can't bolt anything but that piece of kit. If the wording is more generic, ie payload of 30kg with max surface area of 600sq cm then you could attach a mini gun or a expresso machine
So it would be helpful if helicopter manufacturers had interior hard points with a spec that could allow fitting of a wide range of useful kit. 3/8 whitworths dotted around the cabin would be handy.....
Mickjoebill