Yes, basically it becomes able to show neighbour graphics, with slight help of what's drawn behind.
Made "q" shortcut key switching that. If you will turn ON that mode with mouse (this button at left of the palette dropdown), "q" will disable that mode (when pressed), and vice versa. I found it quite helpful.
Can edit 4,4,1 map area, save it, and load. No "map" import yet (it's quite difficult, considering it's in MCD-IDs, while this preview is in PCK-IDs and limited with single MCD set).
Undo is still limited with current tile, after switching it's reset (it will require lots of work to make it all around).
Still not able to work with preview area of size other than 4,4,1 (in todo).
Still no preview cursor of currently selected tile (in long todo, no really need of that).