The api could allow "exporting" pages in the various RSS, and atom
I.e., the output would look like a normal RSS full feed (but you could
also have a parameter for excerpt only, e.g., excerpt=55 (55 words)).
The advantages over plain RSS? Well, via the api one has a very
flexible way to generate the list of pages one wants to export.
And do consider that many programs (well, all I know is WordPress)
have an "Import from RSS" function, but no "Import from MediaWiki"
function, so you would be providing a vital bridge...