Hello, it's that Realation Games developer from http://www.youtube.com/user/RealationGames here! I found myself here from Youtube insight and I thought to join in the conversation to clarify possible speculations...
There is one major down side with the real scope system because it needs another camera for the scope, and that means a lot of more rendered pixels on top of the original stuff.
Because if the player plays on 1920x1080 resolution, there has to be another 512x512 with shader-, postprocessing, etc. effects for the scope also. It will drastically reduce FPS if not compensated by reducing graphical quality for the environment camera.
It can be done efficently if grass/detail objects are hidden for the environement camera which is slightly blurred anyways. Blur shading itself isn't a problem for computers nowadays. DOF shader on the other hand is quite more heavy.
I can't see why it wouldn't work if rendering to texture is possible, just lay another camera render with smaller FOV on the lens, piece of cake.
Optimizing the thing is problem, so I wouldn't blame them not having the real deal with the graphical quality of ARMA.
That sounds like a neat idea, I'll experiment with that someday. I've also thought about mechanic that you need to center the shooters head to the correct position for scope by moving the mouse to move the head.
I myself need also add the distortion effect and heavy motion blur for the scope, they are crucial for the immersion. Also make fully operational optical shadow with the sweet spot.
But hit me up if you have any questions about the mechanics or have any experiments I could fiddle with in my engine to come up with new working innovations.
ARMA definently needs atleast the Project Reality type of sniper scope, animated scope adjustment etc.