The dashed green line is a good suggestion, and something I had considered as a possible indicator. That's more or less what I'm saying: I plan to include a new terrain indicator around a couple of unusual features (holograms and clouds of steam). The details in my post above are simply my suggested treatment. I leave it to you folks to decide A) if you feel the features merit a special treatment in the rules, and B) How to handle it if you do.
I honestly hadn't given much though to interaction with character abilities. For simplicity's sake, you could rule that any effect that negates cover also negates obscurement. While I don't think my proposal is any more complicated at its core than the rules governing low objects (I simply didn't feel like retyping them), Sithborg is right that it would be easier to just treat it as another source of cover.
I suggest letting the defensive bonus from this terrain stack with cover bonuses because they conceptually come from two sources: cover reduces the area of an opponent that you can effectively target, and obscurement makes it harder to see that area. I also suggest it because, as pointed out, it balances the scales a little bit more between melee and ranged units. And finally, I suggest it because it's something new that might inspire new conceptual design in future maps and make the game a little richer; it gives cartographers a little something extra to play around with when balancing a map.
Holograms already exist in several maps; we just haven't had a special terrain option to apply to them. With the game now in the hands of players, this is something for you folks to consider.
Incidentally, I think the game really needs a "Tall Object" terrain type. Objects that serve as walls in most ways, but can be flown over, leapt over, or climbed over by miniatures with appropriate abilities. That's a whole other bag of worms, though; if anyone wants to take a crack at that, I suggest a separate thread.