It would be nice to have an LED shield with 12 or 24 LED's going all around for the end of a stack (so no connector is needed on the LED side.

Yeah that would be neat.

With an option for IR LEDs, I have an application that it would dovetail into very neatly...

I could definitely use this. +1 vote

[TI TLC59116 Datasheet:]

On the topic of the LED board...

The Charlieplexing solution is great but perhaps even fewer pins can be used. By using a TI TLC59116 16-Channel Fm+ I2C-Bus Constant-Current LED Sink Driver ($3.23 and $1.25 in 1000 quantity [TI]), WiFi shield compatibility, Ethernet shield compatibility, Full Motor Shield capability, and other LED shields can be used with displaying different patterns, can be achieved!!

Peter Easton wrote code for using an Arduino to control LEDs using the TI TLC59116. The code can be found at https://github.com/engineertype/TLC59116/blob/master/TLC59116.ino. A posting I found interesting about controlling LEDs with the TI TLC59116 is on the Arduino forum http://forum.arduino.cc/index.php?topic=97134.0

Making a version of this LED shield should be straightforward and there seems to be code for it available in the wild already.

TI TLC59116 Datasheet: http://www.ti.com/lit/ds/slds157d/slds157d.pdf

NOTE: See forum post http://forum.tiny-circuits.com/index.php?topic=170.msg651#msg651 for more ideas.