The BA Sheraton and Park Tower were two properties where Starwood actually owned the building and land so it came along with the acquisition. Marriott just finished selling it off recently since they don't want to own real estate.
Building in Palermo would be difficult for a lot of reasons and Puerto Madero is a good place for a W.
But yes, I'm skeptical on 2024, which seems long to begin with. Considering the economy and other issues in Argentina, more likely 2034. Wish it was open now!