A lot has changed in the year since this was first posted. Lately, I've been thinking about designing an "EFI Shield" for the Arduino DUE. The processor in the DUE is way more capable than any of the chips the MegaSquirt has used, and has native CANbus, so it'd make for an excellent base for a fuel injection controller. Not to mention the price.. $50 for a DUE, I think an EFI shield could be done for around $50-$75 (board plus BOM). Finally have a truely open source fuel injection controller. Way beyond my programming skills, but maybe if the hardware existed, others would join in on the project.
And yeah, not a piggyback, I'm talking stand alone engine management. Fuel, spark, boost, run the whole show.. 