Just wanted to jump in here and give my experience on the topic. I listed a few things recently on eBay, and a couple of the listings had the zoom feature and others did not. No idea why, since the listings were launched at the same time, for the same durations and the photos were similar in size (I tend to take BIG photos!) I did nothing special to the listings that had the zoom feature--it just showed up in some of them at random. Our engineers looked into my account and couldn't pinpoint any reason why this happened.
We're still waiting to hear back from eBay to find out why some listings get the zoom and others don't, even though we're submitting them all in the same manner that we always have. Until then, unfortunately there's nothing we can do on our side to make sure the zoom feature is added to every eligible listing.
Mike will be sure to give you an update when we do hear back from eBay and hopefully get this mystery solved once and for all. I am just as baffled as you all are!