I think of druids and primal magic in general as "spirit magic" to use a more commonly used phrase. I also think that they're going to merge the Feywild and Shadowfell with the Elemetnal Planes to reform the old octohedron Inner Planes, and these fey, elementals and ghosts will serve as the animistic spirits Primal priests rely on for their magic. Which means that the Ethereal will probably choke full of mephit, sprites/pixies, and ghosts hanging around, waiting for a Primal priest to say something.
Heck. Even the druid's Wildshape? That's based on a tradition of donning invoking an animal spirit into your body, reshaping it. Which... is actually kind of why I didn't mind the elemental animal forms of moon druid UA. But that's neither here nor there. If the druid went with a summon-focused build as the shaman, then I would like to see something akin to the Wildfire druid circle's summon for their Channel Nature ability.
As animistic spirits are just feywild+shadowfell+elemental... I can't help but feel that the warlock and sorcerer already are touching on them - wild sorcerer is supposedly feywild-touched, and there's plenty of elemental themed sorcerers. Warlock has fey, genie and shadow pacts already too.
Which brings us to the Shaman. How do we differentiate this class from just a summon-based druid, warlock, or primal sorcerer? Honestly... not sure yet. I kind of want to see what summon spells look like first. But... I am leaning towards a kind of... primal paladin-ranger thing?
Okay, let me explain a bit better. I would want Shaman to have Channel Nature and be a priest. That much is too heavily associated with the name Shaman for me to really accept it otherwise. Full caster + Channel Nature is already covered by the druid. So, that means we can think of Shaman as a primal half-caster with Channel Nature instead of the paladin with divinity.
Half-caster with a focus on weapons is a bit too close to Ranger, so I'd like to emphasize pets and being support instead of using fighting styles and marks or smites.
That's what I would do, anyways.