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I was able to create a script that reached pulses of about 1us or 0.5us based on the example found in mraa/cycle-pwm3.py at master · intel-iot-devkit/mraa · GitHub, in fact here's a screenshot of my logic analyzer getting a pulse of 1us.
Regarding your other issues, you will be able to get Python 3.3 from AlexT's repo. According to mraa v0.9.6 documentation the mraa module can be built for Python 3, so you should be able to use it as long as you build it manually.
If you are interested in using the MCU, indeed it has access to Edison's PWM interface. However, you will not be able to use the MCU with Python as it only works with C/C++. In case you are interested in using the MCU, you should follow this guide.