Improve lazy-load mechanism for procedural code

In Drupal 7, we have two ways to lazy-load procedural code:

1) page callbacks may be placed into an alternate file and loaded on demand via a specification in hook_menu(), theme functions may be lazy-loaded the same way via a specification in hook_theme() (although that seems rather fragile in practice), etc.

2) Hooks may be dynamically loaded via hook_hook_info().

The latter works, but is somewhat brittle and in practice the implementation is clunky. Not lazy-loading procedural code is no longer an option given the size of our codebase, but something more robust than the current hook_hook_info() implementation is necessary.

Discuss. :-) (But not until Drupal 7 is done. Anyone caught discussing this before Drupal 7 ships will be spanked with raw lasagna.)