I love the idea of the mini pet having its own slot on the hero tab. It would help a lot with keeping a cute pet with you and not have to worry about depositing it. I absolutely love the Deposit Collectibles choice by the way!
Something else that maybe Arena Net might like added, they could have expansions to the pet slot in the cash shop, (Maybe a max of 3-5? And everyone normally has 1 slot to start with.) so you could have a number of pets equipped and toggle between each one you want to summon out. That way you can enjoy having a set of your favorites.