It's a tricky business. In terms of raw screen width, we have it. Or do we? Not necessarily on mobile, in portrait orientation.
From a readability/usability perspective, imagine the HN front page being filled top to bottom with titles, some of which go to 150 characters; what would that be like?
(A mock-up could be easily obtained for evaluation; or HN could just experiment with it for a few days.)
Currently, most titles don't strain the existing limit. When we scan the front page now, for instance, there are good many short and medium length titles.
A modest increase, say by +20 characters, might relieve most of the pressure without too many negative effects. Which is to say that maybe the current limit is a bit to the left of the true "sweet spot".
