MMPT probably isn't going to happen for a number of reasons. Amtrak's current station is literally falling apart, so it can't be long before they'll need to move or do extensive renovations.
There are quite a few families around Atlantic Station. The area has changed drastically over the last couple of years. I can't say 17th and Northside is the best block in Atlanta to plop a house on, but it doesn't seem entirely out of place to me--after all, it's between Home Park and Loring Heights. Frankly I think the days of being fearful of raising a child in an urban setting are numbered, but if they had that mindset I think they'd be more worried about the liquor store and strip clubs than the IKEA.
What I really worry about is surface parking or a fortress-like layout that makes the block feel like a shopping center. I think the former is unlikely given the ambitious specs and the small size of the lot... I think this will be dense, but that doesn't mean well-designed (as Atlantic Station's mall proves). On the plus side, the infill will be welcome there, and it sounds very mixed. Maybe this is one project he will actually do well. One can dream
The for sale sign is still at 17th and Northside, so there's no indication that a deal has happened yet. Fall 2016 certainly sounds like a groundbreaking would be imminent, but for all I know it's just an idea that will never be pursued.