Ricoh published two updated Pentax K-mount lens roadmaps on their website:
There are no new products added, just a few updates in the current line-up due to discontinued lenses and the HD PENTAX-DA★ 16-50mm f/2.8 ED PLM AW was moved from “expected” to “current”. It seem that the next lens to be announced will be the HD Pentax-D FA 21mm limited:
Two new Pentax lenses announced: Pentax D FA 21mm Limited and Pentax HD DA* 16-50mm f/2.8
Source: Ricoh
