Three possible street grids have been shown in a document prepared by HRM Staff -
http://www.halifax.ca/RealPropertyPlanning/documents/LayoutsJuly2012.pdf.
The HRM Staff proposed street grid looks like a practical layout.
The idea of a transit terminal has been mentioned. I hope that if a transit terminal is selected that part of the cost will be offset by having it integrated with a highrise building(s).
I think that there is a high likelihood that the decision on the use of the Cogswell Interchange land will probably be based on economics. If the HRM wants to recover the cost of the demolition and restoration of an acceptable street grid then the HRM will probably want to sell the land to developers at a good price. HRM will get the best price for the land if the HRM_by_Design intended height limits are maintained - I sketched the current height limits on the HRM Staff proposed street grid (below).
A Scotia Square type development doesn't have to be the result. A King's Wharf type development would certainly be a plus for the downtown, especially if it housed 1500 residents who will financially support downtown retail (however, it would have to be higher density than King's Wharf since there appears to be less land).
I wonder how much of the land next to the waste water treatment plant is available for development or green space? I think that there were allowances made for expansion of the plant.