Using PHP namespace hybrid for Drupal modules
It looks like there aren't any technical pitfalls. But, using PHP namespacing is not part of Drupal's coding standards. Clive sums it up nicely in a comment on the question:


  Drupal has it's own coding standards which it's best to follow, and namespacing functions isn't part of that. If you're not bothered about the Drupal conventions, then sure, do whatever works for you...but if you're looking to write a module to contribute back to the community, or want it to be understood easily by other Drupal devs in the future, it's best to stick to standards