If I understand correctly how schema.org works (which I’m still not sure I do, even after a using it a few times), the schema for AggregateRating will only work if it is within the scope of a ‘type’. It seems these scope types support AggregateRating:
As it (seems) to be type dependent, I’m not sure it makes sense to support it directly in this plugin as that would involve choosing a particular type, e.g. Product or Service. Not all users of this plugin will be using it for one particular type.
If someone else knows more about schemas and can confirm or deny this, that would help (@vinothkannans?)
You could still add schema support for AggregateRating within the scope of a particular type, by forking this plugin and adding a new file:
the contents of which would look something like one of the existing schema.org markup blocks in the
topics/show.html.erb view e.g. the tags markup.