Thank you for contacting us.
The required feature is not implemented yet, but your second idea is definitely an option. You can include a new page in the administration, in which you can manage the "new categories" - I will tell you what I mean. You can follow these steps:
1. Define a new metafield for your items, that you want to categorize, let's name it newcategory
2. In this metafield, you will assign the values that you can manage through your custom page. Each value can have an order column for example (if you store them in your table) and then you can sort by these column.
Including your custom page can be anywhere in the Admin. Please take a look in the Sitefinity/Admin/Admin.master or Sitefinity/Admin/Modules.aspx. Let us know where exactly you want to have it, so we can tell you which file you can edit.
All the best,
the Telerik team