It would be useful to have the ability to validate addresses inserted by customers against rules that can be defined in the Admin area for each country. Perhaps something like a regex validation.

This would allow for filtering of invalid characters, to validate the syntax in certain countries or in case of international shipping the filtering of entire character sets (i.e. Greek, Cyrillic, Chinese, Japanese). This helps with the creation of shipping labels and especially the latter use case would make it easier for shop owners to ship their products to those countries.