LoneStarMike posted a link to some vague hints at least as to the whereabouts of the forthcoming tower for this lot, reposted here for your inconvenience:
Link to slide presentation (pdf file)
I was glad to see that it most likely won't block the view of the Proper as seen from directly across the Lake or from Cesar Chavez. It looks like Second Street's pedestrian attractions will wrap around it along Shoal Creek, which should be a very nice urban oasis, and from that side of the creek the best-looking side of the library will show beautifully. That's going to be such a sweet area.