Since it is clear that language and content will need to be updated to make this content current and relevant - there should be some standard ways of doing it. My thought right now for shorter texts like the preface is to simply copy and past it so that there are two identical sections - perhaps using Cited format.
New fully editable text
Historic text for reference
In some articles this would be fairly awkward and we may want to have the whole article moved to an updated tool and have the historic text as a separate floating wiki. The floating wiki doesn't have forums linked to it - but that isn't much of an issue if it isn't being directly edited. Alternatively - the text could be just edited directly with the original available in the archive for reference. Hopefully there will be an emerging solution as the project progresses...