luatex depends on mplib built with the lua use flag. As I assume many people aren't using the lua functionality, I'd suggest to make the luatex-dependency optional in the texlive-latex ebuild also with the lua useflag.
not much point in doing only this since texdoc uses texluac which comes from luatex too moreover format.latex.cnf isnt split upstream into pdftex & luatex stuff so as it is now its more or less impossible to make it optional. i'm closing this as upstream but please be sure that patches are welcome.
