I'm going to Kickstart a project this month called PeX, which stands for Peripheral eXpansion. A home page is taking shape here: http://bit.ly/1kwvXez
It's shaped like an X with an Arduino UNO socket on each limb, as well as a socket for RasPi Expansion board and a Xbee wireless module (on each limb). It'll fit a Pi and an Arduino Uno simultaneously as well as another two expansions. At this stage one of the limbs will have a Beagle Board cape socket, but this is being considered for removal as a cost saving. You can put breadboard or Kluge circuits in the arm-pits, or develop your own oversized expansions to plug in over that space. All of these are connected with an FPGA but this is not the focus of the board, and you won't have to learn or use the FPGA unless you want to use it's capabilities (which will be impressive.) To this end all the FPGA sources will be in Schematic format 1st, with a Verilog version for the textually adventurous.
You could: - use your Arduino with three Shields - use your Arduino with three Pi Expansions or a mix'n'match of the two - get really big projects together - add a Raspberry Pi to an existing Arduino project (after porting it to PeX) to give your project a UI/GUI using the PI's HDMI out, and USB Host for keyboard/mouse as an example, or quickly add IP networking - (best of all) take advantage of the cheap and superior range of LCDs available for Beagle Board. For example the 4.3" Cape and 4.3" Pi LCD boards from Sparkfun are $60 and $145 respectively. Code will be devloped for the FPGA to abstract the LCD and provide a nice easy SPI interface to the Arduino - avoid a Rube Goldberg Kluge ball of string nightmare when crossing over hardware system lines of demarcation
Would you buy it? Between $130 and $160. To make it cheaper I'm considering a smaller FPGA (Cyclone IV 10KLE vs Cyclone V 25KLE), and removing the BB Cape socket. Would love feedback on how valuable those points are to you.
Please leave me your feedback and stop me before I launch a Kickstarter for a board no one wants :-) All comments appreciated no matter how vile and upsetting.