A preview of the newest functionality was showned during the latest webinar: adding your own maps in TerraIndex via the .KML format.
You can add a KML map in the project detail screen by adding it as an attachment to the project (new column in the project details).
You open this own map layer by opening the map and scrolling down in the layer selection. The KML maps (which are attached as attachments) are visible here. With the check marks you switch the map layer on and off, just like you are used to with the other map layers. (Note: this attached map is for now only visible in TerraIndex Web; not yet in the tablet App)
Adding a KML file is the start for uploading multiple types of files to the project.
Where can I create a KML map layer?
In the different CAD and GIS packages you choose the layout type for the map. You export this from the CAD or GIS package as a .KML file.
I only get a KMZ file (from ArcGIS). What now?
A KMZ file is a zipped KML file. You can extract the KMZ file with (for example) winzip.