The only real limits are:
RF front end/IF section (if any, could be a direct conversion)
The latter really only comes into play for high datarate/frequency work, so its all in the (hopefully replaceable) front end.
I wouldn't call that last update list up to date:)
C++ is at C++11 (2011)
Objective-C arguably is at a new version due to weak references and ARC (which are a feature of the compiler) (2011).
PHP has had updates (for better or for worse)
Its all an arms race in speed. However, if people were smart and realized that hashing was never a good solution and instead followed something like PBKDF2 with a large C (thousands of rounds), we still would be safe.
Most portable? OpenGL. Has the benefit of not requiring huge libraries ala Qt. Consider sticking to OpenGL ES 2.0.
Most useful? Quartz/CoreGraphics. Not a portable choice of course, but a good drawing toolkit none the less.
Or, in reality, every skimmer records numbers. The thief comes by with the "dumper", buys some gas while take a complete download of the current recorder memory. Its far less risky on the retrieval of the numbers, especially if the skimmers have already been identified and the cops are waiting around the corner for the guys to come back (unlikely, but you never know).