Some nice ideas. This was my post from awhile back:
https://us.forums.blizzard.com/en/wow/t/guardian-shaman/655399
The rune thing has been done with Death Knight, and it didn’t really work out too well. It became very complicated to manage and a lot of people wouldn’t play it because they would be starved of a particular rune, making it impossible to play ‘how they wanted’. They’ve obviously iterated on it and its much better (or rather simple; I preferred it how it was). So I doubt they’ll go down that path again.
It feels like this is more of a design for a Diablo Support Shaman, and the runes would be more ‘passive’ based on which elements you call to your aid or something. With set bonus’ you could potentially have all elementals and bonus’ available etc…
For WoW, I think the tank Shaman would primarily be Earth, but would have access to fire/wind/water for small buffs and damage fillers. I don’t think they would make a major part of the spec.