At each generation of page it could be nice to write the files in the standard cache and in a second directory (called incremental cache). The cache strategy would never delete the incremental cache. In this way we would have an incremental cache that would be available in case of very high traffic.
We would be sure to have up to date the most viewed pages.

Then the webmasteur would be able to play with vhost to change cache.
the pages that are never viewed won't be in the cache but they are never viewed so who would ask a page that is never viewed !!

This is a cheap and nice solution for having a critical cache of most of the pages .

This directory would be configurable in the admin of the CMS like the cache.

It may be interesting to delete pages that are older than x days, may be, this functionnality can be integrated in the CMS with a ON/OFF or with a shell script.