This is already happening:

- Sony Pictures Imageworks open sourced Open Shading Language, Field3D, Alembic and OpenColorIO.

- Pixar opensourced OpenSubDiv

- Disney opensourced Ptex, BRDF Explorer, SeExpr and Partio

- Dreamworks open sourced OpenVDB

I wouldn't be too suprised if we would see an open source renderer within the next 10 years, especially if SPI is going to replace their in-house version of the Arnold renderer, as open source software has been extremely successful for SPI.