As much as I love Ryzom, the problem - and the benefit - it had over the past few years is that there are not as many players on the world as in the "big" online games. While this has more benefits imho than drawbacks, the one obvious drawback is that "fan servers" would divide up that small number even more.
If you follow the Ryzom forums then you might have noticed the odd post in the past weeks where characters (e.g. Thaxl on Leanon) posted that they have developed their own extensions to the world and are privately running their own server. These servers are not released to the public for various reasons (dividing up the community, maintenance work required, support work required, open and unconstructive criticism etc.)
Even the source code is open I believe it is essential to the Ryzom game to keep the player base united on as few servers as possible. The Language barrier is a good reason for the three servers we have right now. Maybe a chinese server would be a good add-on, tapping into the potential fan-developers there.
Update Mar 2013 (some of which might be slightly off-topic):
In September 2012 the game saw a server merge. The one remaining server has a much higher population than any single one had in 2012. After some initial issues of the merge have been sorted through, active roleplay picks up again. Shortly after the merge an official announcement followed, shutting down the Ryzom Ring - support for player created content. The reason given was the financial costs of running a second server to host those Ring instances. This is relevant to this question because it hints to the complexity and cost of running a server publicly.
Meanwhile, the Ryzom Core development website moved to http://www.ryzomcore.org and Matt Raykowski posted a great write-up of where Ryzom stores all its data which is extremely helpful in running your own server.
There also is a fully open source game being written based on Ryzom's source code: Tempest in the Aether. So by now more people may be running servers with the NeL engine, some with Ryzom, some with other game(s).