Expat 2.0.0 will enter testing soon. The new version of expat breaks library compatibility with older versions, so quite a few recompiles are needed.
By the time expat 2.0.0 gets into testing, the known packages which need recompile have been recompiled. Please report bugs against packages in current, extra and unstable that need a recompile to work with expat 2.0.0 when you find them.