ToME WikiKhymChanur: I've gotten into the habit of Mathoming all of the non-random artifacts that I'm not going to use, and it sometimes bugs me that I can't do this as a Lost Soul while in the Halls. So the idea came to me of a 'Souvenir Bag' artifact that Lost Souls could start with. Activating it would give you access to Mathom House, like the Rod Tip of Home Summoning does for your house, but with 0% failure rate and no recharging time. If you don't care about Mathoming artifacts, you can just drop it to free up an inventory slot.
TheArchivist: I love this idea! I'm the same way, Mathoming amusing junkarts.
Circaea: Could you implement this as a power instead of an item? Then no inventory slot would get used.
Sirrocco: Personally, I like the idea that there would be a (small) cost associated with it. Gives the vanity factor a bit more punch. It's not just that you're mathoming amusing junkarts - it's that you're actually devoting a (quite small) bit of player power to the ability to mathom junkarts.