If you haven't noticed yet, the Ultra Dex for Gen V has already been posted in the URPG Battles forum.
New features include Dream World Ability and Story Rank classification.
Improvements include BM/MT/SMs being listed for all stages of Pokemon (instead of the previous See ??? for BM/MT/SM), and better, more accurate ability descriptions. Note that those ability descriptions are still the shorter versions. You would have to refer to the list of abilities in Reffing Encyclopedia or Smogon to find out the detailed explanation of an ability.
This thread will serve as a discussion, suggestion, and reporting thread. For any suggestions on the Ultra Dex (eg. new features to add), they can be posted here. For any mistakes that you found or spotted, feel free to post here so that we can make the appropriate edits, in making the Ultra Dex one step closer towards perfection.