I appreciate the fact that the "Slide In" plugin includes filters to allow for modification to its default behavior. However, I think there is some room for improvement in how some of these filters are implemented.
As a specific example, take the "wdsi_get_related_posts" function: https://gist.github.com/JCPry/39d2f802f38173c1e4b1#file-functions-php. There's a double filter on the final return statement, and no way to filter the WP_Query args before the query is run. This means that if you want to customize the query, you have to run an additional query just to get the results that you want.
Here is a modified form of that particular function, which I think would be a better use of filters: https://gist.github.com/JCPry/39d2f802f38173c1e4b1#file-functions-replacement-php