Hmm, yes there are some interesting things out there. I still haven't found a pain-free method of getting the wikipedia xml to an ebook format, though it presumably can be done. One method might be to convert the wikipedia XML to HTML and then to epub, perhaps filtering out some stuff like sidebars along the way. Then gzip the whole thing and use FBReaderJ to read the one big gzip file on android. It seems a little long winded to me, but otherwise I don't see how delving into the details of wikipedia xml or epub can be avoided, which might get very complex.
See also a similar discussion where they had storage problems that don't appear to have been solved:
https://www.mobileread.com/forums/showthread.php?t=31041