If we examine the phenomena of Open Source; both in the software arena of Linux, and the RPG market of d20; is that the open source model does not give anyone say over the quality or quantity of the Open Source being distributed.
Instead of focusing on chaos that is Linux, consider FreeBSD, which is under an even more anarchic and laissez-faire license than Linux. It has the highest reputation for quality, and was chosen by Apple to be the core of Mac OSX. You can't claim FreeBSD is shoddy or that Apple isn't making any money. The difference between Linux and BSD isn't so much the license, as it is the community behind them.
I for one do not want to see just anyone come along and decide they can produce Harn material. I think it is a mistake.
But that's what we already have! Whether or not Harn goes open source, as long as fans have the permission to produce fanon, then fanon will be produced! If I can produce fanon without NRC or CGI standing over my shoulder, then anyone can. Sheesh.
While iinteresting, I personally think that open sourcing Harn would only work so long as there was a "gentleman's agreement" on quality and who does what. However, if you get a "spoiler" in the mix who refuses to play by the "gentleman's agreement" there is nothing you can do about it except refuse to buy his products.
But we don't have that "gentleman's agreement" now, but we still manage to get very high quality fanon with little or no spoilers. If you're concerned about bad quality stuff from ICE, SJG, etc, then consider the power of the trademark. You don't get the "Hârn Approved" stamp unless approved by CGI/NRC. This could be similar to the d20 stamp, but with some oversight. If the quality of commercial stuff got too bad, we discriminating customers would just refuse to buy stuff without that stamp.