Renderings of BIG-Designed Two World Trade Center Revealed
The earliest stacked-box skyscraper design that I know of is within Arquitectonica's Capital Park West (1983).
In many ways, Arquitectonica can be considered the ur-OMA spinoff. Remember, Spears and Koolhaas worked together just before Arquitectonica (and OMA) was formed. And, while Capital Park West was never executed, they were nonetheless the first architects to get 'delirious New York' type architecture built, well before Koolhaas and Zenghelis themselves.
Thus I now wonder whether BIG's WTC2 will be the first stacked-box skyscraper actually built. I'm trying to think of some other such project(s) that already exists, but I'm drawing a blank--please let me know if there is. I know H&dM's NYC luxury hi-rise currently under construction, but that's a bit more voxelation than stacked-box, and there's, of course, the New Museum, but that's not really a skyscraper.
Arquitectonica's Capital Park West is clearly a decendent of Leonidov's Dom Narkomtjazjprom project.