The xz package has been part of Sage for about three months (see
Trac#21063). Making it stanrd would simplify handling of tarballs (see
Trac#18236), and of R (standard package in Sage, see
Trac#20523).
Using xz to solve the latter implies to make zx a standard package. As pointed out by T. Scrim, this should be discussed on sage-devel. Quod facio...
Speak now or forever hold your peace...
--
Emmanuel Charpentier