There are many streets across the "upper" city that would have become one-ways too, if the original plan had extended that far. I find it funny that most of the complaints about the one-way system seem to come from "suburban" drivers -- they would not want that setup in their own areas, but also seem to oppose its removal and are very used to driving through the city relatively unimpeded.
Two-ways definitely won't lead to immediate benefits, and not everywhere -- it will take other urban improvements. But it's been almost 70 years since the one-way system was implemented, for an urban area with a different set of land uses and travel patterns. One-way streets have their applications, but context does matter, and overall for the network's needs the system is out of date. And I agree that once King loses lanes for LRT (and its construction) Main's gain of westbound flow will be important.
Barton is narrow and much needs to be done to make it a more "complete" street. I think Barton's decline had much do with loss of employment and employed people in the neighbourhoods nearby. Much of it is now one-lane each way between Victoria and Lottridge, and I can see its "diet" extended east and westward, but the planning issues are many and it will take decades for change.
It'll be interesting to see what happens when King is transformed by LRT, and whether the city will take the opportunity to do something smart along (and between) nearby parallel routes.
Agreed on all points. I would also not attribute Barton's decline to its street design alone, far from it- though it certainly accelerated things. I do think streetscape improvements alone will help the street tie together the slow but steady regeneration of adjacent neighbourhoods better than it is already-- its somewhat suppressed right now. But I suppose you could say the same for many other streets.
I'm not so sure travel patterns have changed dramatically as much as certain segments have shrank (industrial workers, trucks) while others have grown. The fundamental patterns seem quite unlikely to budge; Hamilton's geography will always dictate (limit) its movements in ways that can't be avoided (as with any great city

). People have, and probably always will, go over Burlington Heights or the Beach strip to cross the Lake in 1000 years, and travel will likely always need to be closely managed in the lower city. But I digress.
Insofar as what's coming, I will add that King and Main are true outliers in that they are, or at least should be, almost identical in terms of function to the old city streets of Toronto, or King street Waterloo, or what have you. However, pedestrians seem to actively avoid them by contrast- its on clear display with the Strava heatmap:
King-Main:
Take your pick in Toronto here of Bloor, College, Dundas, Queen, King, etc:
And King between Uptown 'Loo and Downtown Kitchener (since "we arent Toronto"):
So, big and noticeable change is on the horizon I'd say. There are lots more inferences one could make from all this, but I will present without further thoughts for now.
The City has no plans to convert Victoria or Wellington beyond what they have already done AFAIK.
Even here, Main is going to remain primarily an eastbound road. I think it's necessary in the lens that the LRT is basically going to delete most traffic capacity on King St - Main St needs to absorb some of that westbound traffic.
Yes, they don't, and the rationale for Main is pretty straightforward. My point is simply that it is easy to lose sight of things and point at one-ways as the problem themselves, and so we should always be cautious of letting things go too far, as Hamilton tends to do- especially as the city inevitably and truly re-urbanizes again. Discourse can help establish that understanding; Vic/Wellington are merely a good example for showing their utility (if a bit too wide), imo.