Damn, I was hoping to keep this quiet until I had more information. Ok here's what I got:
Sold by Fresh Direct to Atlas like you said. It's currently leased to Fresh Direct until January so they can finish moving to the Bronx location.
Site is currently too small to build a stadium and parking, they'd have to buy out that space behind it which is currently LIRR property.
That's where it gets messy. It's not being used by the LIRR as far as I can tell, I'm not aware of any trains that run through that portion of track. It was mostly used for industrial transportation and they could remove the tracks there without affecting LIRR or anything else really. But the state would have to approve it since it's MTA owned and MTA is run by the state.
Cuomo and the Governor hate each other so it would be pretty tough, but at the same time Cuomo may see it as a way to stick it to the mayor. I've been monitoring it since the deed transfer went up. If you guys are interested I'll post the rest of the documents I already have.