I have tried many knowledge base tools, including those from Zendesk. They'll all have one thing in common: they do not provide a desktop app like Evernote does. While I have managed to build a small knowledge base in Evernote (for anyone who's interested, this is what it looks like), it is far from ideal (branding, no native support for menu's), but actually, it is quite manageable.
The knowledge base has to be simple; just like the knowledge base created by Evernote itself (link). We need to be able to create categories and a homepage (or menu) to provide quick access to the right articles. Since Evernote already has a feature to publish articles on the web, the main development goal is to offer an interface to drag and drop categories, articles and introductory text.
I think this solution will fit most businesses, while it can be sold as an Enterprise product. It is something I'm particularly interested in as I use Evernote for all of our stuff, including tips and tricks on our business accounting. Being able to manage our customer knowledge base from inside the app, will make it the only note taking app I will probably use.
I'm wondering if Evernote feels something for the idea to implement this feature in the long-term strategy of the Business suite. It is, like I said, already 'there'. It has to be developed a little further.