While fixing bugs on the sci-mathematics/maxima package, I noticed the ppc keyword was apparently dropped from versions later than 5.9.1 without explanation. I suspect this was a mistake. Maybe you want to readd it? I know Michael Hanselmann (hansmi) tested the package on ppc before.
marked ~ppc when fixing #111062 (I disagree that this has a significant dependence on Bug #127927, since that one only triggered when gnuplot is emerged with -doc, and I couldn't get it to reproduce even then...)