We know that the item cache is deleted after every patch, so this suggestion is about providing a pre-populated item cache as part of the patch.
The reason behind this suggestion is that addons like AtlasLoot or like mine (Altoholic), cannot rely on the accuracy of GetItemInfo as the item might not be in the cache. Querying the server to get item information is thus required, and there's a risk of being disconnected if done too often.
For instance, an addon like mine allows the user to find upgrades for his equipment, thus if we assume he's looking at upgrades for level 28 gear, he might potentially find upgrades in gnomeregan.. but if the item id's are unknown, the addon won't return them as potential upgrades.
Thus the idea would be to have a cache that already contains a lot of item id's, obviously not the most recent additions (like the most recent pvp season, or the latest raid dungeon), since I assume Blizzard wants to prevent data mining, but a solid selection of items such as all instance blues & above would certainly help, and would not require any code change in the wow client.
The same idea could be applied to spells, especially those that relate to professions.