Ideal stretch goals for me would be models that are not already available in some form and 3d elements for the board. I've been an avid player of Knight models Batman Miniature game since the beginning(nearly 5 years now). As more of a miniature gamer than board gamer what will really sell this for me are elements like 3d scatter terrain( cars, barricades, lamp posts) that aren't necessary to play the game but will add a miniature, skirmish game feel. Also models that Knight Models has not already released. The Oracle model was a good start. How about also including:
-Various "Elseworlds" Batmen
-Scarface & the Ventriloquist
-Man Bat
-KGBeast
-David & Cassandra "Batgirl" Cain
Also Themed Story Expansions like Knightfall or No Man's Land. I can see unique play boards (like snowy, urban desolation for NML) and they could include unique characters specific to that storyline