I'd like to have access to templates and other transcluded pages, pre-transclusion (and before subtransclusions take place), so that I may do some rendering modifications on the wikitext in a context sensitive manner. There is currently no way to do this as far as I know. I relate this to the ParserAfterStrip hook that is called on source documents before templates and other variables are expanded. I'm sure such a hook could also be useful to the community at large for other purposes. Poking at the code, I've found that I can insert a hook near the end of the braceSubstitution function in Parser.php and have it work as intended (though I haven't done any exhaustive testing).