1. Amazon is (already) leasing a big building in Seaport. It's mostly Alexa, ~500-1k staff.
2. Amazon is shopping cities for a 50k-person second headquarters; one candidate site is the old Suffolk Downs in revere.
For many reasons, i hope (2) does not come to pass.
There's a building in Fort Point, but apparently they're looking to lease yet another one. 
And the winter.
I went back last year in October. 20 years is a long time, but the traffic now reminds me of Manhattan (apparently the bad drivers are called Mass-holes), with screaming cabbies and bumper cars.
I did have the best clam chowder of my entire life there, so there is that.
Not everyone wants to move to the Bay Area. I for one am one of those people.
My own employer is HQ'd in the Bay Area, and without their office being here they'd be missing out on my meager skillset.
The same is true of most of my coworkers; they don't want to live in the Bay Area. Some did a tour in the Bay to get a good name on their resume, but they've paid their dues and now want to live where they want to live.
Amazon is headquartered in Seattle, not the Bay. I think they have some tiny satellite office in Palo Alto.
Amazon is a polarizing force, for sure. Some locals are concerned that their presence will drive up the cost of living further. Others want the broader economic impacts introduced by more tech jobs.