Shadow lairs are kind of stale, so I figured it wouldn't be the worst idea to revamp them. Specifically, I'd love to see your wonderful new level-design skills copy pasting some of those other levels together.

How do you mean?

Take 6 levels, one for each monster family, and revamp them to have swarm themed enemies spawn occasionally, more block puzzles, you know, the usual new content scenario. No need to expand the land mass or even add new scenary beyond turning on the occasional swarm themed black floating blocks. Add 4 rotations of the 6 "new" levels on a ? block to each shadow lair. All of this takes place on the fabulous shadow lair depth, whatever that may be, with all red boxes, giving more loot than ever before. The price of the key easily makes up for this.

You may also wish to touch up the levels themselves. I suggest adding swarm turrets and the occasional swarm themed enemy to them. No big deal.

But I don't have time to do this! I need to be making prize boxes!

I certainly agree.. I would then like to point out that:

A) You're going to be releasing jewel prize boxes, which don't require more than the old color swap

B) You can release a shadow lair themed box! Wow!

Swarm Prize Box:
50%- Shadow Lair Key
30%- The usual armors/accessories, this time black+red
10%- Some interesting swarm themed recolours, monkey tails, dragon wings, gear halos, etc.
8%- Corrupt Eyes- http://imgur.com/lh8b8e9, See- http://forums.spiralknights.com/en/node/102314
2%- Swarm Aura- Take hacked aura. Replace the things that pop up with squares. Play with it a bit.