Most of the 3D viewers work with some sots of inscripted communication with the browser but it seems there are indeed tools available that decript this communication and hens getting the model data out as it went in (however cannot confirm or prove this information is correct).
what I do as precaution is simply capturing my desktop with a video screen capture (Nvidia experience) tool and upload that to vimeo and add this as a link for visual presentation. This also has advantage that I can use full quality settings in Marmoset Toolbag (the software I use for the real-time previewing) and get full advantage of my powerful GPU to make the best quality preview possible.
You can get an impression of how that looks here (https://www.cgtrader.com/3d-models/various/various-models/3d-crystals) click the blue vimeo button to get the preview running.
Almost all of my products are accompanied now with this type of preview and my Vimeo statistics show almost every visitor makes use of them so I think its a good strategy for boosting presentation or compensating for the loss of the 3D viewers.
Keep up the good works fellows and have fun ;-)