Market Share of Open Source Hardware
2019
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.
2017
Prusa Printers is doing $33M in revenue - [1]
2013
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.
https://www.sparkfun.com/news/599
OSE Work
OSE is working to increase the fraction of open source hardware available in the world. See Open Source Leadership Summit Presentation for current results.