Is this something that we want to have before the launch, right after the launch, or whenever it is ready?
Tagging is just a poor man's
version of classing, since it doesn't let you define the relationship
between tags. True that you can put any task in several projects/tags, the
problem is that the project structure is nevertheless flat:
Which will become cumbersome to navigate for occasional visitors as the
number of projects goes up.
Sure, but after years of Bugzilla we have also seen that the rigid tree structure of https://bugzilla.wikimedia.org/describecomponents.cgi causes many problems too, and occasional visitors probably find it cumbersome anyway.
If we want a high level overview of the projects, we can always have a wiki page identifying the main teams/projects, the starting points to understand the hundreds of projects that we will have soon. Now there is a task to discuss this. :)