Welcome to the Q&A Forum

Most cases like these are catered for on an adhoc basis, usually done by a dev team that will migrate the entire database into the new site.

There could well be a market for a porting tool that provides a checklist type system for a large scale site migration. I have seen site migrations go wrong. A lot of revenue can be lost through the plummet of organic traffic from a failed migration.

Just to confirm what my findings discovered, it showed that Wikipedia does (or at least did then) actually provide value from an SEO sense. The external links are indeed nofollow however Google could be wavering the nofollow status of those links because of the fact it is "Wikipedia".