This would be an awesome idea! I don't know how they would implement it, but I can already see how players would be able to load up their current skin and then click on any of the hats, wands and maybe pets which would show how it'll look like on them.
How I imagine it is that it would be somewhat similar to those Minecraft Skin Editors on those skin sites where you're able to move the player around to see how the skin looks. This is also seen in the Potterworld Player Profiles too.
Another similar idea is to add the Hats, Wands, and Pets that a player currently owns into the forum's Player Profile page and maybe show what type of hat or wand the player is currently using.