How do I flag and categorize Drupal Commerce related products? Given that there isn't a related products contrib module yet.

What is the canonical means (with priority of maintainability, developer experience) to flag related products and thus have them displayed in views ? 

Would it include setting up content types with many different taxonomy vocabulary fields? Another product reference field?
The core taxonomy module offers a flexible system for sorting content. You can easily build views based on content type and taxonomy.