The free market will reign supreme. The idea of it being the tallest will fade away in the sense of symbolic purposes. If anything, its temporary.
I'd look to the Midtown East Rezoning and the parcels that WILL be purchased and added onto. When you purchase a property worth several billion (as land is tight), you can sure bet something much larger will rise. 270 Park for example. 270 Park being a more extreme example as it will be demolished and something will rise in its place, but I can envision a lot of renovations with addition components (minus the demo for financial reasons). In other words, turning class B space into A, and retrofitting a whole tower while adding floors to it. Could vary based on the wishes of those property owners or stakeholders, but its a start.
Just the first of many.
