When the set of official dwarf planets is expected to increase or new bodies considered for inclusion?
As I noted in a previous answer, the official body for naming and classification of astronomical objects is the International Astronomical Union, or IAU. They are the ones responsible for designating bodies as "planets," "dwarf planets," etc. The scientific community recognizes them and their decisions as "official."
The IAU meets periodically for General Assemblies to discuss general issue; the next such meeting is scheduled for 2015. The topics discussed may range widely, covering all sub-fields of astronomy. Unfortunately, I don't know the exact topics for discussion, and while I imagine there will be a wide range, issues relating to dwarf planets may not be covered. However, the IAU does meet in between these meetings to discuss a variet of topics.
That might answer your question, but if you're talking about the possible discovery of dwarf-planet-like bodies, I can't help you. There are probably many on-going efforts to search for small bodies within our solar system, but I don't know of any recent discoveries of possible dwarf planet candidates.
I hope this helps.