From a quick check of the current top 10 entries on http://biogems.info/ many are missing the licence metadata in their gemspec files as shown on https://rubygems.org/gems/
e.g.
For people which care about open source, having a licence column would help. For space this could be reduced to an icon, e.g. "?" for missing metadata, "green tick" for OSI approved licences, or "..." for other? Or simply a yes/no boolean for if there is a licence specified in the metadata?