Post-2007 is post-2007. It's not "in 2007". It's not "in one year after 2007". Does the concept of post-PC include wearable computing? By the aforementioned standards, it would seem to me personally that no -- it would have to be strictly relating to the devices being introduced along with the term 'post-PC'.
Does a requirement 'Windows XP or later' mean the program will run on Vista, 7 and 8.x? How about '512mb RAM or more'? Apart from extreme cases (Windows 3.1-or-later programs running on 64-bit Windows 8), I think we can agree that more is better.
But let's say that people will truly think 'oh, it's just things added in 2008'. How about "numerous features introduced to language and language runtime after 2007, supporting even additions in 2013"?
Not really pleasant. I still think Objective-C 2.0 is more concise than the above contraption. If anything, even "features from Objective-C 2.0 and later" sounds way better than the above.
I definitely wouldn't go with anything like Objective-C+ARC since I, for one, don't think ARC is nearly as an important addition to the language as @synthesize. And five years from now, any arguments against naming it relative to Objective-C 2.0 will stand against naming it Objective-C+ARC or similar.