Personally I think this is overthought. Hasn't Brandon said that the thing with the Sibling is less complicated than is being theorised?
Couldn't it be as simple as:
- The sibling is slumbering in Shinovar for some reason or another, thus their reverence of stone. The shin know a good deal about this deity, and know more or less why it is slumbering (radiants broke their oaths and hurt or drained it in some way).
- When they asked the "Spirit of Stones" before declaring Szeth truthless, they were looking for a reply from a spirit that wouldn't respond because it is slumbering/dormant/hibernating.
Didn't Rysn's interlude in WoK have a story about people worshiping a king who had actually died and they didn't admit/realise it?? Would be an interesting hint without being too literal.
- Then: "Let's consult the oracle/god to see if this guy is a Radiant or Truthless." "Ah, the oracle/god still slumbers. He's the god of the Radiant's tower, so if they were back he would have woken up." "Sorry Szeth son son Vallero, here's your oath stone."
Also, it seems clear that the Shin are not nomadic, as they have their land (which was cultivated just for them to live on) closed off to most of the world.