Wouldn't it be better to move the section concerning migration shorten to the content which only applies to wikispace specifically, create a global migration How-to page, move it there and put a link to this page here. So we don't have to write the same text for every wiki farm which has been shut down or will in the future?
Topic on Talk:Wikispaces/Flow
All of that section is specific to Wikispaces, except the one line with links to the two related generic topics. A global "So you want to switch to MediaWiki?" page would certainly be nice, not sure how much useful information it could contain though.
I guess, that might be helpful. From there we could link back to the other wiki farm's migration How to's in their own articles. So it works additionally like a kind of overview.