Market Share of Open Source Hardware
Prusa Printers alone is doing about $72M revenue if the 8000 printers/month figure is correct (personal conversation with Josef Prusa). Lulzbot is growing significantly ($21M in 2018). Overall open source hardware appears to be around $200M.
Prusa Printers is doing $33M in revenue - 
As of 2013, the market share of open hardware (by OSHWA definition) enterprises was about $100M, or about one millionth of the global 100 trillion dollar economy. Sparkfun was the largest open source hardware company, about $30M in revenue. Other notable enterprises include Adafruit Industries, Arduino, Raspberry Pi, Lulzbot, and DIY Drones. Many more are not open according to the OSHWA definition.
OSE is working to increase the fraction of open source collaboration towards economic ends, thereby increasing the fraction of open source hardware available in the world. See Open Source Leadership Summit Presentation for current results. Open source hardware, and open collaboration in general - is a fringe phenomenon today, comprising about one millionth of current economic activity. In practical terms, collaboration does not exist in economics.