Kahn did supposedly have a hand in the Kaufmann building, but I think it was a more minor work than the Dominion Rubber plant.
I'm fiercely (i.e. chain myself to wall) supportive of preserving both buildings. Fortunately, Kaufman is preserved permanently thanks to its stunningly successful (all sold out!) condo conversion. It's fortunate that it's a pretty universally attractive building, and it's got a fabulous prominent location.
Dominion Rubber is obviously not in quite such a good place, but it's at least it's occupied. It's obviously not going to look like it's in the best shape, but I guarantee it's rock solid. The Uniroyal plant in Detroit, almost exactly identical to the Kitchener plant and also designed by Kahn, was demolished a few years ago after a long abandonment. It was built so solidly that it took almost a year and bankrupted the demolition company.
My father was (briefly) the last occupant of the Forsyth building when I was quite young. I ran around that place, and it was a world of adventure for a kid. There was a pretty impressive office area, wood paneling and all. I was terribly sad to see it go.
Another childhood architectural adventure was the Kaufman's Zeidler-designed house. They were almost never home, so kids would often play in the backyard and explore all around the place. It's a bit of a strange house. Not really Zeidler's best work, but certainly interesting. It was in some danger a few years ago, but that's a long story.
Krug Furniture is still doing remarkably well. In fact, so well that I could see them potentially moving to a more modern, presumably suburban location. In that case their building would also be prime for a conversion. If VIA's service didn't suck so severely, it would be great for commuters.
The restoration of the Bauer building in Waterloo has been taking absolutely forever. Vincenzo's, an extremely successful Italian food store, will be the anchor tenant. I think they were supposed to have moved in by now. The problems are with contamination.
From what I've heard, the Lang Tannery (once the largest in the Empire!) is 100% leased. There was a story on its remarkable resurgence in the Record a few years ago. I think a paintball arena might be in there, among other things. Artists' studios, weird businesses, etc.
The factory at Duke and Shanly (Electrohome) is a neat one because it's so tucked away in a residential neighbourhood. There are a bunch of those scattered around Kitchener. There's one on Mansion in the East Ward.