So what could be cached on CDN? Front page? Every thread and page therefore? Some other pages?

Now how to keep these up-to-date as new posts comes and ensure that they stay in sync? What about pages if you have comments there? Looking at code it seems "1 hours ago" is in the html, so would need some javascript or something to dynamically calculate that too..

Seems, much more fragile and error prone system compared to what is in use.