Earliest code injection for caching

Grahack

I'm thinking about a very simple cache system for Vanilla. That's why I'd like to inject some code at the earliest stage of the execution.
First let me tell you that I'm still discovering the inners of our forum engine... so I may say silly things.

So, noobily, I looked for the earliest place where I could do a delegate call.
After some investigations, it appeared that:
If I want to write my cache thing in an extension, its code must be read, so the delegate call must be after

// INCLUDE EXTENSIONS
include($Configuration['APPLICATION_PATH'].'conf/extensions.php');

in appg/init_vanilla.php
and even after a call to GetDelegatesFromContext() that we see few lines after.

My questions:
- to me, too much processing is done before the extensions inclusion (instanciating page objects, js and css inclusion, session handling...), is there a good reason to include extensions after those actions ?
- how to inject code as early as possible, without changing the core files and break the actual extension philosophy ?

EDIT: with my VeryFirstDelegate, I need a VeryLastDelegate
EDIT EDIT: VeryLastDelegate seems to be PostRender in the PageEnd class