The solaris forks are definitly not dead. What became of opensolaris is now known as illumos and there are quite a few specialized illumos distributions around like SmartOS, OmniOS, OpenIndiana, Nexenta Stor and a few more.

I agree that you need a community of users and developers for a successful open-source project. Luckily in addition to the companies like Joyent, OmniTI, Nexenta, Lucera, Delphix (who all actually do a lot of drivers development) there is a friendly and growing community of volunteers that contribute.

What is sadly sometimes lacking a bit is marketing. After oracle went closed again many assumed opensolaris died, but in fact a lot of interesting systems development is happening in illumos land. Of course all open source. I wish a few more people would recognize what a great system and community SmartOS and OmniOS have.