Much like other limited time events, this event would be on a rotation and last a week or less. During this time, item drops from treasure boxes would be boosted tremendously, allowing players to find various items they may never have found the time or resources to acquire.
For the duration of this event, the following would be in play:
+ red treasure boxes would replace green treasure boxes at a higher rate*
+ item drops would be increased tremendously, dropping at a rate of 1.5% for red boxes, and 1% for green boxes (subject to change)*
+ orbs of alchemy drops have a 50% chance to be replaced with an item drop*
+ fire crystals dropped during this event will be doubled
+ heat obtained during this event will be doubled
+ all energy gates only need 1 energy to be opened rather than 3
+ new arcade gates would have a higher chance at ??? depths, and the final depth of all non-boss strata would be an ensured treasure vault
+ Basil would have an additional 5 recipes in stock at every terminal
*arcade exclusive
This sort of event would get people into the arcade and hunting down boxes, and also encourage opening up danger rooms and energy gates. This is also an amazing opportunity to introduce a handful of new weapons to the public in a rare controlled setting (such as promotional items from times past and perhaps new items in general). This sort of change would be breathe a new life into the arcade, as every box you open can have an item in it that you can either sell or get excited over, and at a rate this high, you will be able to accumulate a nice little arsenal.
If new items are introduced, I would also suggest adding a recipe for them onto the auction house. This allows players who wish to create and supply others with these items to do so, and allow items to be created via teamwork from the community (also a use for all these dang orbs).
This is probably the best suggestion I've seen in a while. This kind of event can really make the game live hard during that weekend, and breath new life into it... plus it's a great way to draw in new players.
A few interesting variants of this I can think of-
Dangerous Weekend = All danger missions available; all arcade enemy stats are buffed; enemy crown drops are tripled
Optional: Dangerous and Hazardous prize boxes are given for completing danger missions
Throwback Weekend = All levels cost 10 energy again; Fire crystals and orbs drop A LOT more frequently
Optional: Minerals can be deposited once again for crowns and to build gates that rotate every hour
Oddly Specific Weekend = A featured level set or monster family grants 3x crowns
Optional: Killing monsters of that family/from that level give special tokens that unlock that monster's armor set
Explosive Weekend = All knights are sent a set of expiring blast bombs, heated to level 10; blast bombs on sale in supply depot
Optional: This could be used to test new weapons, or done for any weapon really... see neutralizer