Modder Reyhard has recently added a 3D 'PiP' scope proof-of-concept to RHS:Escalation (and KoffeinFlummi of ACE/BWMod has done work on something comparable using 2D optics);

https://www.youtube.com/watch?v=0InO2wOGYyc
https://www.youtube.com/watch?v=1QbMFyYO8U4

Reyhard's implementation is already very impressive and highly usable with a surprisingly low performance impact. The biggest problem with it at the moment is that it's an application that really demands the best possible PIPQuality setting however when used in a vehicle with multiple other PiP mirrors/viewports performance then suffers unacceptably.

I wonder if it would be possible to implement *two* PIPQuality settings linked to some property of the class/vehicle implementing the surface (even if the second quality level could only be set by editing arma.cfg). In this way it would be possible to have the highest quality rendering for such a critical application and low (or none) selected for less important purposes like mirrors.