Yes, you are right it isn’t trucks that are a barrier towards two way conversions of King and Main it's also regular car traffic. Majority of the traffic on Main and King are people getting on and off the 403 to and from East Hamilton/Stoney Creek. We have to admit King and Main is basically an expressway with synchronized lighting and has more lanes than RHVP does. They'll be far more car population coming out of Main St than RHVP will ever produce.
Eventually less and less cars and trucks will be using Main and King because of RHVP and two way conversion will be more viable, therefore helping to revitalize the inner city. It isn't happening now because there's way too much car traffic that uses the Main and King St.
I think it's an overstatement calling King and Main an "expressway". The Linc is an expressway; you can cross the city on it in seven or eight minutes. No one parks on it, there are no lights (synchronized lights are great, as long as you catch the bounce), there's no one turning off side streets onto it... I think they're streamlined, yeah, but they're nothing like an expressway. And there's no place for one downtown anyway.
Up on the Mountain, it's different. There's still room for some development, there's nothing anyone really has to tear down that's going to be upsetting (of course, there are ALWAYS people who find a reason), and the airport's there. To me, it has all the elements to reshape Hamilton.
Toronto used to have lots of heavy industry, right up to the 60s. I used to ride the train through its remnants every day 10 or 12 years ago... big fields of broken brick like you'd see in
Roger & Me, only in Toronto (and, admittedly, on a smaller scale). Heavy industry moved out of Toronto, and light industry ringed the city, out where distribution was easier. The inner city didn't die... it became something else. Hamilton wants that chance. The steel industry there is never going to be what it was in the 70s... it's more and more automated and it just doesn't supply the jobs it used to. But there are half a million people there, and they need to make a living. They're at the edge of a Great Lake, on the nexus between Canada and the US. All they need is the infrastructure, and it's finally coming together. I've heard that medical industry is particularly interested, mainly because McMaster's there. Now if they can viably make and ship pharmaceuticals from that location, it could completely change the nature of the city. The revenues from new industry and jobs, shepherded properly, can bring about the gentrification of Hamilton's downtown the same way it did Toronto's. Apparently there's already an art colony forming around James Street.
I don't mean to suggest all this is to be laid at the feet of the completion of one new road. What I do say is that this is an ongoing transformation of one of our major cities, and that the addition of the expressway is one of a number of strategic items necessary to facilitate it. What happens next, what they make of the advantages they have in location and what they've built, depends on the people of Hamilton and the politicians they elect.