All they show is an eye, which is Jack's eye from the opening shot of the series. There was no additional filming. I just think some people are reading too much into it. It's not Juliet's eye, so it doesn't mean that she's really alive. It doesn't necessarily mean that season 6 will start in the same place as season 1, with a rebooted timeline. It's advertising.
Perhaps you visit other boards where people do, but none of us here think that the eye is a scene or a shot from next season. None of us here think season 6 will open with that same eye shot either. It's a simple symbolic gesture for season six and nothing more. I thought it was very effective and powerful following the last scene of the finale & the S6 promo.
Vogs, thanks for that advertising post info. I was trying to find ways to say what you said and you said it perfectly.