It's probably been suggested numerous times but I'd like to see a testing zone where players can attack combat dummies and see the effects of their weapons. There would be a break-down of their hit and damage statistics (e.g., by base damage, crit percentage, etc). The dummies would have some alterable characteristics (DR, AC, HP, saves, and a timer, for example). This would, for example, allow the player to set the number of HPs, and a timer, for say, 3 minutes, and then swing away. At the end of the timer (or 0 HP), the hit statistics pop up. The player would engage the dummy by entering an instance (so not everyone is just going crazy in the same room against the same dummies). But the player who starts an instance should have the option of making it private, or leaving 1-5 more slots open so any other player could jump into the instance (or enter the instance with a party already formed). Players in the Testing Zone (but not in a test instance) would see a list of test instances with open slots, or be able to start their own instance.

Also, the Testing Zone should have a weapon lending/borrowing feature. Any character in the area should be able to lend any weapon in inventory to another player in the Testing Zone. A lent weapon is marked as "lent" but still takes up an inventory slot. The receiving player gets the weapon in inventory and it is marked "borrowed". Proficiencies, race restrictions and minimum level still apply. A player who has lent a weapon may recall it (un-lend) it at any time. A player who has borrowed a weapon may return it at any time. If a player with a lent or borrowed weapon leaves the Testing Zone, all lent and borrowed weapons return to their owners.

This is probably so far from ever being realized, but I think it would be useful and fun.