Hi,sebastien,
We have Eagle library with all connectors, but only a few kinds used in our product. We have 2-pins , 3-pins and 4-pins with buckle.
NOW we use unified 4-pins (2.0mm) MOLEX type for our new electronic brick extension shield - STEM. It has SPI connector on STEM. We will sale Chassis v1.1 if customers have needs; we are also developing serial LCD driver for LCD1602 which is 4-pins compatibe with STEM.
In my opinion, it really just of exposing specific connectors which can simplify the hardware design for users sake.
GOOD luck with your electronic brick extension shield for Jaluino, we are look forward to it!!