It was suggest in another thread that it might be useful to discuss how one might add connectors for added I/O capabilities of other processors, like ARM, etc. So, here is the new thread to discuss such things! 
I've been doing a lot of thinking on how connections for additional I/Os might be added to an Arduino form factor board. My suggestion is to put added connectors on the outside of the existing Arduino compatible I/O connectors. New boards might have to be a little bit larger to allow the space to add these connectors, but adding them on the inside would affect project and board space too much.
You bet I would like to see added special connectors for I2C, SPI, CAN (if available), to make it easier to connect to these buses. It simply makes sense. Right angle connectors could be used where there is space for them to connect outward.
There would have to be a survey done to see what connections for each processor type might be added. Maybe a common set of connections can be defined that boards could use and extended shields could connect with. Using the smaller 64 to 100 pin packages should be workable in a design like this.
Let's discuss it! 
8-Dale