The way things are at the moment, TW5 under node.js only supports a single wiki at a time. You could run multiple instances, each pointing at a different wiki directory, but they would have to listen on separate ports without some additional configuration.
At this point, TW5 isn't intended to be a real, solid, multi-user HTTP server because that stuff is incredibly hard to get right - and of course we've already got TiddlyWeb, which benefits from 3 years of use in the field.
Instead, the HTTP support is designed to support two primary scenarios:
* running an instance of TW5 on your own PC/Mac/Linux fielding requests from a local browser. This gets around the issues with saving changes when running the single file version on modern browsers, and makes it easier to do things like offer storage of individual tiddlers in separate files, improve drag-and-drop binary file support, and so on. I'm hoping that we'll be able to offer a simple GUI wrapper for the node.js version which will make it a one click install to get up and running
* running a private instance of TW5 in the cloud. It should be possible to use something like CloudSmith Stack Hammer to offer a one-click install to, say, Amazon's EC2 servers. The idea would be to use the host security features to limit access to the instance, and then use TW5 batch publishing facilities to maintain a static copy of the site on Amazon's S3 static web service
Returning to your original question, I do therefore think that TW5 will need support for multiple wikis at once, to allow for flexible implementation of those two scenarios, but I haven't given it much thought. What sort of scenarios did you have in mind?
Best wishes
Jeremy