I think that it would be a good move to make a Requirement object. Then in the future it would be easier to add queries based on that. ie. Find all gems with a specific requirement, find gems with no external dependencies. This would help users if they want to find pure ruby gems for instance. It would also make for a nice place to hang behavior later.

Serialized objects don't work well for queries and writing a migration later would be harder than doing this now.