To hold a database of mods that can be searched and filtered easily
What got me onto this was the sudden boom of mods and modders (as of 2014-05-03 there are 64 mods on PAMM). The current solution is to use PAMM to browse and install mods, with links to threads for each mod on the Uber modding forum. This works to a point, but will get more and more cumbersome as the mod count explodes. When the modding API matures I expect the growth to accelerate further; and again when the server is released; and yet again when the game is officially released. An easy-to-use interface for finding mods is a step in the right direction.
To be a detailed source of information on Planetary Annihilation mods
Some mods are complex in nature, and deserve to be explained in detail (looking at you PA Stats, and the various frameworks). I want content that explains how everything works fully. Long-term that's what I hope this site will generate.
To help players get into using mods
I feel many players would use mods if they knew what mods can do for the game. Many people don't frequent the Uber forums, or the steam forums, or even realise that mods are available. A website focused on mods may raise awareness.
To help new modders get modding
Some time in the future the plan is to have a modding api reference section (maybe when the game is officially released and there is a stable api to reference). Other than that, guides and tutorials may make their way on site over time.