Not sure if this was intended so take it as an FYI, if nothing else.
Latest package I got that showed json-c dependency:
bind-9.10.3_P3-x86_64-1.txz
I see the changelog of Wed Jan 13 00:01:23 UTC 2016 added json-c for pulseaudio.
Oh, see this if interested:
https://bugs.gentoo.org/show_bug.cgi?id=525362