This is precisely my take. I wasn't familiar with SFW until last night (this post), but I've been playing around with this concept for awhile myself.
The only real drawback that I'm seeing so far is some link fragility. There are two countering forces at work here. You can take a link to someone else's content and mirror it back to your own SFW. If the source content changes and you don't take the "pull," your content is no longer relevant. This might mean for popular sources, lots of replicated copies of the source, but not always current. There is also a problem with the always available aspect. If someone is using content from another source, what do you do when the source goes down or just changes locations. At least with a non-federated wiki, the entire set of content goes offline together. That model is less prone to rot since it prunes entire branches and not just bits and pieces.
The only real drawback that I'm seeing so far is some link fragility. There are two countering forces at work here. You can take a link to someone else's content and mirror it back to your own SFW. If the source content changes and you don't take the "pull," your content is no longer relevant. This might mean for popular sources, lots of replicated copies of the source, but not always current. There is also a problem with the always available aspect. If someone is using content from another source, what do you do when the source goes down or just changes locations. At least with a non-federated wiki, the entire set of content goes offline together. That model is less prone to rot since it prunes entire branches and not just bits and pieces.