As of matplotlib 1.1.0, qt python bindings can be provided just as well by pyside, as they were by PyQt4 before. In my opinion, before such alternative is added, bug 369127 should be fixed.
now implemented in 1.1.0.
As bug 369127 has been recently resolved, the alternative dep should be pyside[X] too (well, perhaps something a bit more complicated till pyside 1.1.0 hits stable).