Yesterday, I touched on the Shared Stash changes and how it could be used as a business opportunity to monetize slot size upgrades and many other in-game "services".

For example, if Blizzard were to make the gold-collecting pets an extremely rare drop, they would then be sold on the RMAH. Those pets are extremely useful in-game and would be highly sought after. In essence, you're paying for a gold collection service using real cash.

I liked the idea so much, that I've decided to expand upon it.

Here are a collection of virtual items that could have low drop rates, forcing them to be sold on the Real Money Auction House:

• Items or Scrolls that magically increased your Stash, Shared Stash, and Bag Space slots. For example, a "Scroll of Minor Bag Space" that increases your slots by 3.
• Rare summon scrolls for those gold collecting pets.
• Even more rare summoning scrolls that summon pets that gain +10% gold. Just like the Daeity pet. (Blizzard, hint hint.)
• Vendor potions that increase your selling or buying prices for a fixed time or fixed number of items.
• Salvaging potions that improve salvage results for a fixed time or fixed number of items. Same for better enchants, gems, etc.
• Remove Experience Shrines, and instead have rare "+15% XP Gain" potions.
• Rare potions of Magic Find and Gold Find that complement your gear. These would be time based spells (e.g. 30 minutes.)
• Collecting multiple rare potions that can be mixed together to create new and improved effects.
• Selling "normal" Paid Services but as virtual items instead. Like Paid Name Changes, but using the RMAH instead.
• A portal scroll (like in Torchlight) where the player is transported to a small zone with above average loot and/or a guaranteed rare spawn. Because players might be paying $1-5 for something like this, it's sort of their version of DLC since it's an area inaccessible to most players unless they purchase it.
• The return of the Nephalem Cube and the Cauldron of Jordan, except that they're rare drops, they're tiered, and they require rare "upgrades". For example, you can only break down level 10 items when you get the initial item. You purchase pieces or upgrades to the item on the RMAH, and then you can break down up-to level 20 items, etc. Sort of like a cash sink vs gold sink.
• Mailbox upgrade items. Several items that allow you to upgrade your personal mailbox and it's appearance. Allows you to send more items at once and lowers postage fees.

If you have any other clever ideas for a paid in-game "service" (like experience gain, more cash, or faster travel), let me know and I might add it. :)

These items are so useful, especially for farmers and hardcore RMAH users, that Blizzard doesn't even have to restrict the items or try to force users to sell them on the RMAH. They'll be so rare and useful that they'll ALWAYS end up on the RMAH.

Other than "services", the Diablo 3 developer team has also been working through multiple iterations of the rune system. Skills could easily be bought from vendors, learned, or be personalized, but I think their intention is to make Runes sellable on the RMAH. The highest tiered runes will only be available on the RMAH, unless you're really lucky. This forces users to pay (in cash) to get new skills. I think this was the main reason why they have been having so many rune problems.. they've been forced to monetize the skill system, which significantly limits their creativity.

* UPDATE:

On February 7, 2012 Bashiok was posed the question about the removal of items (like scrolls) from the game, and if Blizzard planned on monetizing them in any way.

His response was:

@WilliamCairns1 We didn’t remove them so we could charge people for them later, if that’s your question.

So, this is the Blizzard Promise™. The Cauldron, Cube, ID scrolls, summoning scrolls, etc. will NOT be item drops when they return, players will get them for free (they won't cost gold or cash), and they will be "soulbound" (cannot be traded in any way.)