As a CPAN author over a few years, I concur with the sentiments here.

Top-level namespaces should be used sparingly. If there is a good reason to use one, it is what it is, and should provide the ability/availability to allow a whole host of sub namespaces.

Naming something at the top-level because you think it'll "sell" is not appropriate (although it goes through unchecked). When in doubt, send your desired namespace to modules <at> cpan.org, and see what they think of it. If you're going under something else, such as App::, do your own due diligence, ensure it doesn't collide, ensure it makes sense, ask here for reflection, then do it.

Always, doing due diligence in your path selection is desired, and you're respected here for doing just that.