All,
I've come up with a way to creating aliases for tiddlers, in what I think is a clean and fairly intuitive manner. Using a field named "aliases" as a list field, I've updated the navigator widget to first check if the target exists, and then if it doesn't exist, if it is in the alias field of any tiddler. If it is an alias for just one tiddler it navigates directly to that tiddler. If it's an alias for multiple tiddlers, it displays a missing tiddler template which includes a disambiguation section listing the multiple things it is an alias for. Finally, I've updated the link widget to determine whether it is an alias for just one tiddler, and render it as existing if so.
Check out the attached file for an example.
Matt