I do have some related (possibly silly) questions/thoughts:
What is (was?) the main intention of the *subst* feature of MediaWiki templates?
Is subst meant to help reduce parse time or is subst intended as an editorial tool?
Currently, the user input containing the subst keyword is lost when the user saves a page. Are there any plans/intentions/ideas to store this input somewhere?
Would it be feasible to have a compilation like model for some templates (something like an expanded subst mechanism)? Could/should we store pages (revisions?) at the "templates expanded" level?
As an observation, the current template system in some aspects violates the revertability paradigm of MediaWiki, as all article revisions (not only the newest) are affected by changes in an included template.
--Ligulem