Hi @lunatio,
Those mockups look nice! I’ll pass the idea on to our product team, which is looking into this issue currently.
For what it’s worth, the reason why we’re still using the iframe is because the last time we ran an A/B test on the iframe (a year or so ago), there was a significant decrease in conversion when the iframe and “buy now” button was removed (meaning fewer item sales). Our analysis showed that once a user navigated away from Market to the author’s preview site, they didn’t know how to get back and actually purchase the item. Some authors include a link back to the item page, but most do not. “Frame escape” code (which no longer works) or instructions will have a similar effect.
The iframe is obviously not an elegant solution, and as browser vendors move to more secure-by-default positions, it will only get worse. We have both product and development folks looking into a better solution now, and when we’ve got something to announce there’ll be a post here on the forums.
Until then, thank you for your continued patience, and all we can suggest is to set SameSite=None on your demo sites if you need cookie behavior.