I just committed a change to move 7 previously closed drivers in Nevada to the open source tree under usr/src. This change involved nothing more than Makefile and copyright block editing, so it was pretty much a no-brainer. (Though the heavy lifting of the legal review had already been done.)
The drivers moved were: bscv, bscbus, i2bsc, gptwo_cpu, gptwocfg, todstarcat, and todm5819p_rmc.
Admittedly, none of these are likely to exist on your hardware, but it does help to have more bits open. Hopefully someday /usr/closed will either cease to exist or become its own consolidation separate from Nevada.