Already done! Just look at the wiki site...bottom left for printing options!
At the AmiWest2015 Devcon, one attendee brought his printed rkm to show and tell.
Either i'm stupid (highly likely!) or this feature isn't as great as I first thought.
Each small section of the wiki has to be exported separately as a PDF or added section by section to the book creator wizard before exporting and printing.
Would be nice to just go to lulu.com, click buy and then receive several hefty manuals in the post.