Well they got new models in the End times, which were more or less the first AoS releases. Same goes for Death and Skaven. The Glottkin book was released bit over two years ago, which in "Army book update time" is not a long time.
In any case, new daemons and maybe similar set as Tzaangor are quite safe bet for the Death guard, so an update for AoS is quite safe bet soon.