I know it's been 5 months but I'm now pretty close to getting the next version out of the door. There's been other, more major, problems to be solved around the underlying maps APIs (see http://wordpress.org/support/topic/disappearing-map?replies=7) which has taken all of this time, when I've been able to work on this.
So the next question that springs to mind is what information from the checkin metadata do you want to be able to use in a filter hook and how?
The reason I ask is that the plugin already has a filter,
wp_quadratum_strapline that is passed the content of the strapline that appears under the map in the widget. The filter hook function currently is passed the checkin's venue URL and name and the checkin's timestamp.
Based on our earlier discussions I can add the entire geolocation metadata from the checkin as well as the URL to the venue's icon to this filter, which should give you all you asked for, but is this the right filter for what you envisage using this data for? Or is there a need, in your mind, for another filter that passes this information and if so, what content do you want to the filter to pass to the hook function and act on?