That lot between Aqua and BCBS has come up a few times here (I've paid attention because I work in BCBS) but there hasn't been any real activity announced or even rumored there as I recall. I and a few others have said it would be nice as a grand staircase or something to gently transition between upper Columbus and the lower level street, which could improve the pedestrian experience and bring human beings down to those storefronts. But in the real world, there hasn't been a peep. The land is probably worth too much to use it as a piece of private civic infrastructure. Though the residents of Aqua probably have enough pull that a tower there would have to protect views.
Edit: just happened to have a photo handy that I took a while ago in case it should ever come up again.
That's BCBS plaza property on the left wall, Aqua property on the right, and Columbus in the back. Any construction would have to stay clear of all of those things, since Magellan owns none of them.