In the QIIME 2 2018.2 release, Metadata supports optional column typing, allowing users to declare a metadata column “categorical” or “numeric”. Using optional column typing, columns that look “numeric” can be declared to be “categorical”, allowing the columns to be used in categorical analyses such as alpha-group-significance.
There are a number of other changes to QIIME 2 Metadata in the 2018.2 release. See this forum announcement for details on what changed, as well as the updated Metadata tutorial. 