Network-wide categories for products

I've been looking all over this place for a solution on this but didn't find anything so instead of reviving a 2 year-old thread I'm posting this as a new issue.

I would like my users to use site-wide categories when creating a new product.
I'm not interested in just displaying all the categories from all the "sub-sites" on the main site. Instead I would like global taxonomy tables on the db so that ALL users can select and enrich the global categories.
On wordpress-mu there used to be an option called global_terms which eould create a new table on the db called sitecategories. Unfortunately when wpmu was merged with "vanilla" wordpress thus creating wordpress 3, these options were deprecated and removed from code.

Any ideas on how to bring this feature back to life? It would really make our marketplaces shine!