This is very similar to (in fact, I’m pretty sure it’s based on) the patches that were made for 1.0.3 and 1.0.4 and are discussed here
http://modxcms.com/forums/index.php/topic,49153.0.html and a video here
http://www.youtube.com/watch?v=SUbM_D2GT4s
Basically this embedded version appears to work the same way; your included file (using @INCLUDE filename in the input options value field) can use javascript and save complex and multiple item input to JSON. This doesn’t generate a popup, it is embedded directly in the editing space for the TV. So you can build an entire mini-application in a TV.
The code for the TV is in a textarea (or a text input, I suppose, if it’s not going to be very much) that can be hidden via css, and all the user interactive stuff is there below the textarea, and some javascript can be used to automatically update the data in the textarea for the save; much like the configuration properties interface for snippets and plugins. The interactive functionality is up to you; drag-and-drop, text entry, whatever floats your boat
Of course, your output snippets will have to cope with the data you save, be it JSON or text or however you chose to save the data. Ditto tpls could get interesting, I suspect.