There is literally only one feature that I miss in 4.1.2 and that's the new notifications API introduced in 4.3 that allows third party apps to clear notifications. It's pretty annoying it took them so long to add that functionality to Android but other than that, I'm fine with 4.1.2 really.
It's ridiculously implausible to consider that Samsung would release an official 4.3 update... Now that the phone is 2 years old and no longer in production, Samsung wont even consider dedicating any resources to this task considering the S5 is gonna launch soon. Srry to be a downer, but it's not happening. But on the bright side, there'll be plenty of stable custom ROMs for 4.3 not to mention that i'm already running 4.4 omni
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