Taking away the product group code field has really limited customers and the Item Category
The key on the item category could be the Code and the Parent Category not just the code.
Since the product group code was removed we have customers that the item category is a major issue based on how it is setup. The customers were using the item category and product group as separate item categorizations and filters.
Attributes do not work well as they are very limited in scope of where they exist and can be used as filters. The item category hierarchy also has major filtering issues (there is an existing ides for this one)

For example this is a typical customer setup (when they had the product group)
Top level Item (Parent) Categories of
Steel
Plastic
Wood

Then inside each of these the customer would like to have the same subcategories in each one (this was their product group code)
Brackets
Supports
etc.

This is not possible since you can only have the category Brackets once so when a database is upgraded the categories create as Brackets1, Brackets2, etc.
The customer needs to be able to filter in various areas of the application like
Filter
all wood parts
all brackets
all wood brackets

This is not possible with he way the table is setup and how the filtering functionality works in BC.