You have the option of adding a custom view to faceted search to show your custom property. Depending on your Alfresco version the approach of configuratively adding the property to the default view might also (still) work.
Unfortunately the limitation with the faceted search is with the data that is returned by the search API. The search APIs that are used only return a subset of data (the data that was originally required for the pre-faceted search page). So only some of the properties are returned. In fact pretty much all the data returned by the search API for each result is already displayed.
It would be very easy to construct new views or augment existing views with additional data if your updated the search APIs - however, this will require you to override the search APIs defined on the repository that are called.
So in summary, your customization options are limited by the REST API and not by the UI.
In RM, we extend the search API to return additional metadata to the faceted search page in order to allow us to do exactly what you described. I explained the approach in my session at BeeCon earlier this year and at a Alfresco Day last year. My slides are linked from this page Alfresco presentations I've given. I'll see if I can dig out my notes and transfer them to a blog post on the topic later, if that'd be useful?
I would appreciate if you can point me to the code where you have extended the OOTB search api to return back custom fields. I am trying to do similar stuff for one of our client.
Retrieving data ...