This isn't a limitation of WordPress. It's a limitation in the stack. The average WordPress (or any other CMS for that matter) stack doesn't serve pages from R

This isn't a limitation of WordPress. It's a limitation in the stack. The average WordPress (or any other CMS for that matter) stack doesn't serve pages from RAM. And even if it did, it could expire, it could be updated, it could become corrupt, the caching server could go down, or have a number of other things go wrong. There would be a call to the DB, the DB could fail and there would STILL be a static html page returned providing information on the error.