Richard,
This is one huge question. As most replies so far have hinted at, this
is about human process engineering (hmm, isn't that what much of CS is
about anyway?)
You will need a human process in there - a mechanism to actually carry
out the reviews. If you don't have that, if there are no ongoing
resources to keep the U+1F4A9 under control, any automated process to
put it into review will fail. Of course, once you have the resource
lined up, you will need the mechanism to feed it. Kind of chicken and
egg here.
But first, I would ask a far more important question. Why do you need
300k pages on an intranet? Just how big is this organisation? What is
the business purpose of the intranet? Is it a repository of old crap
that no one will throw away, or is it a real, accurate and usable
resource? The first thing to do with that pile of pages is to get each
one to justify its existence. Set the rules for what the site is
supposed to be achieving and make sure every piece of content is serving
a purpose. Once you have done that, and got the site down into the low
5-figures, those same criteria, adapted over time as the organisations
goals and objectives evolve, can be applied as part of the review process.
One thing I would like to implement on that sort of scale is a digital
linking of goals to objectives to user actions to content; then as any
of those validation points is achieved or becomes obsolete, the content
that was present because it jumped through those specific hoops can be
removed unless it can prove itself against the organisations evolved
paradigms.
Rick