I've had two conversations on enwiki in the last few months where it has been desirable to change the image shown in a page preview to something that is not what the tool identifies as the first image in an article. For simplicity: imagine that we don't have an image of Actor X, but midway down their article we talk about their comedy duo work with Actor Y (pictured) and so Actor Y is shown in the Page Preview, clearly misleading as the person doesn't match the name. The only solutions are getting a picture of Actor X (could be literally impossible) or removing all images from the article (could be very undesirable). At least, those are the only solutions I'm aware of.
To me the obvious solution would be a magic word or something that we can encapsulate in a template so that I can write {{PagePreview|None}} to have no image in the page preview, and ideally I can also write {{PagePreview|Image.jpg}} to override the first image as preview and instead use Image.jpg.
It is hugely undesirable for the only solution to be changing the primary rendered article layout in order to accommodate for a secondary layout feature like Page Previews.
I'd be delighted, of course, if there is any other solution and I'm just not aware of it, so please correct me if I'm mistaken.
(Please ping me or do something that gives me a cross-wiki notification so I'll notice replies to this.)