bms001:
Future developments
Add range finder and/or barometer for altitude hold
My suggestion would be for you to use a LiDAR Lite V3 for rangefinding - so much more reliable and easy to use compared to a barometer. I use one myself for my Arduino RC airplane.
bms001:
Re-make on Teensy or RaspberryPi and add significant ‘autonomous’ functionality e.g. GPS
Do yourself a favor and go with the Teensy (if you want to do image processing, you'd want to use both a Teensy and a RPi together - Teensy for control and RPi for image processing and then have them communicate via UART or I2C).