I'd like an addon that can answer questions about my socketed gear:

Which soulbound gear has empty sockets?
Which of my gear has sockets with sub-standard gems? (eg. Blue gear with Green quality gems.)

Essentially I want a to-do list of things I need to gem-shop for.

It might also be useful to show, for a given socket, what guild assets are available to fill it, both in gems and in crafting recipes. Given the database-extraction system used by the Missing Recipes addon, one could even show all gems, guild-craftable gems, and guild-possessed gems.