From what I've been told, Burnie can expand. But government that owns Tasports doesn't want to spend money in Burnie. Its more a political issue if anything.
Having attended a talk given by a senior Port Authority official, the wish is to have Burnie, the Bulk Port, Devonport Cement and Ferry, Bell Bay, Containers, Hobart , Antartica and Cruise ships. Unfortunately before amalgamation of the ports the Port of Burnie struck a deal for 15 years or so that lowered the cost of transporting containers through Burnie which no other port at that time had any knowledge of hence the loss of container shipping from Bell Bay. Once this agreement runs out you may see Tasports Master Plan fufilled unless parochial interests intervene. Bell Bay is the second deepest port in Tasmania following Hobart. Personally I believe Bass Straight ships need to get a lot larger to get economy of scale, look at the tiny little Searoad ships that operate out of Devonport, possibly one of the reasons why Bass straight is one of the dearest pieces of water to ship across in the world.