2. With 5 stacks of NV buff, Diablo can randomly drop (~5% chance) a special drill that can add sockets into weapons or armors. Number of sockets added randomly ranges from 1 to max. no. of that part, e.g. 3 for a chest pieces. The items with sockets cannot be drilled. This adds importance of the final boss, Diablo!
3. To fulfill pt 1 & 2, at least 1-2 new areas & 3-5 packs of elites should be added in act 4. This adds variety in farming act 4.
4. To list an item in AH, 5% of buyout or base price (whichever is higher) is reserved first. When the item is cancelled or no one bids after 36 hours, the listing fee is charged. When the item was traded, the listing fee is returned but 10% of final price was charged instead. This can lower the base price and facilitate the activities in AH, letting more players participate. The item won't be listed in huge number with no one is actually bidding. If the item is godly, the market will push the price up.