We're planning (read: really want to but might not have time to do everything initially) to target a wide range of programming environments, with Scratch as a really basic level; This would make Marty a kinda smart toy, being able to do logo-like things but not much more. The more complex approaches will of course allow a lot more to be done with Marty.
The control board itself is going to have a fair amount of smarts, with an ARM cortex M4 - but that'll be running our firmware, so playing with that would require somewhat in-depth mbed experience. We'd expect most people to use the i2c or serial interface to hack with Marty, by writing their own code on a microcontroller, RasPi or BeagleBone, and packing that in with our board. As it's all open source, adding to the firmware will be possible, just not the most beginner friendly thing.
As for the WiFi functionality, we're looking at the ESP8266, (not final but unlikely to change) and building a C++, Python and ROS (http://ros.org, serious robotics stuff, very cool) set of APIs to use with Marty.
tl:dr; Two types of control, _standalone_ with an added raspi/arduino/other microcontroller, and _wifi-connected_ to a program running on a computer (scratch, python, C++...)