Almost any vanity pet fanatic will tell you that one of the hardest things to do is deciding what to delete to make room for your newest little friend, or which pet to take out of the bank and parade about when heading out to quest, grind, or raid. The idea of making vanity pets easier to store and carry has been one that's been a perennial topic of the suggestion boards and an issue dear to the hearts of every pet fanatic who's set up elaborate trade agreements with the other faction or spent countless hours in Zangarmarsh just to make sure they got ALL the vanity pets possible, and it looks as if Blizzard has finally answered their prayers.
The leatherworking supplies bag is a bit harder to pin down. We already have a leatherworking bag category, so this may be simply a shuffling of data.
As far as a soulbound items bag goes, if it simply allows any type of soulbound item or gear, and comes in sizes greater than the current 18 slot standard, this could be great salvation for any class who carries around an extra set of gear for various situations, be they a Druid with tank, DPS, and healing sets, or a raider with various resist sets.
Of course, we can't say for sure yet if these new categories will be used right away for Sunwell loot or recipes, or whether they're simply in reserve for possible future use, but the prospect of more bag space has this druid drooling.