Yi's mirrorless MFT, according to reviews as I don't own one, are half the price of competing models. I have a panasonic G10, but I'am watching Yi...
Have you watched the people that use Action cams? Drones, Dirtbikes, Mountain Bikes, Kayaking and more... A warranty doesn't generally cover "Smashed into building buttress at high rate of speed whilst attached my 250mm racing drone, will you please replace under warranty?"
It seems that most people have settled for smartphones for the bulk of their photographic needs. When you can get a similarly spec'd action cam or MFT cam for 1/2 or even 1/3 the price, a LOT of people will jump on that. Especially people that have broken a GoPro... Ask me how I know that :)
DJI has a lot of competition just getting started... The quadcopter world is absolutely on fire and moving amazingly fast.