Predictions of imminent collapse are being made all the time. The reason you don't see them is you don't look in the places they are being made, and they don't receive media coverage. Because they are indistinguishable from eye-twitch crazy.

In the same way that warnings about bigger conspiracies look increasingly crazy, warnings about more imminent collapse get lost in the sea of other 'mental' predictions.

Even if you do go looking for such predictions, distinguishing them from the crazy stuff that surrounds them is not easy. They would look exactly like the noise that surrounds them. Plus, in such forums, a medium-term collapse production based around something so mundane as climate change is passé.

Specific timelines are both hard to predict and kookbait.

Dig at the limits and collapse lit and you'll find qite the range of plausible estimates, ranging from 20 years ago to millions of years from now.

Far more useful is understanding methodologies and rationales. Those, if sound, offer more useful guidance.

The collapse will be caused by the realization of what is coming rather than global warming itself. Everyone still has their heads in the sand but once people start waking up it will cause panic.

That's possible. I've suspected the death of cities such as Miami will come not from a storm, but rather from loss of insurance on buildings as people realize what the next big storm will do (in 20 years or so)

I'm not sure that's the scenario the OP had in mind though. A realization of crisis could also have the opposite effect. I think our main problem now is that we're not panicking enough. Humans tend to do decently well in crises, often the only time we solve certain problems.