BYD is already selling more (PH)EV cars globally than Tesla in 2015 (rather amazing, since BYD has a clear focus on China for passenger cars for now!).
BYD also has a profitable second global EV business in buses/specialized vehicles.
The move to more (PH)EVs in China is already happening without Tesla. BYD is currently selling more PHEVs in one month than Tesla is selling EVs all year in China:
EV Sales: China
And neither the BYD Qin nor the BYD Tang are exactly "cheap" vehicles.
Tesla is nowhere without a local partner/manufacturing site - and the Chinese government heavily favors domestic car and EV companies.
Tesla is years behind in China - and that gap will not close until the company has local manufacturing JVs and local battery sourcing in place (I highly doubt shipping cells from Nevada ever makes them competitive in China).