Don,
My intention is that only reusable include chunks would live in the forum-core/lib (which, as you point out, is already the case in some packages)... I didn't mean to give the impression that datamodel or tcl api would move there as well!
.LRN does use some aspects of this approach and does benefit from pages being factored into reusable includes. One difference though is that .LRN portlets require the original package interface to be mounted somewhere.
In many ways this TIP is about officially endorsing an approach that is already becoming the norm before I undertake a significant refactoring of forums.
