There are not many choices within the harbour.
The only future problems with Halterm and larger vessels are truck traffic, length of wharf and water depth.
Truck traffic can be solved in the way I described.
HRM and the port authority have to quickly find a solution as any future terminal would not be open when Cogswell closes. Or HRM delays Cogswell for several years until the port makes a decision.
The wharf can be lengthened at the expense of the filling in a portion of the small beach.
The wharf can be expanded to the east without fill and provide increased water depth without being affected by rising sea level.
Moving across to Dartmouth would require a huge amount of fill and the rail line is well above the water.
And in shipping, time is money and moving to Shearwater is a negative in comparison with other locations.
For more information look at the charts; here is an excellent source from a graduate of NSCOGS :
http://www.heathergabrielsmith.ca/ma.../halifax2.html
Be sure to explore her website.