The usefulness of Primal Ancients will depend on what comes next.
For Ancients the introduction of the LoN set added many new build possibilities to the game. I think it's ok when an Ancient item drops, I like it when its an upgrade, but I really appreciate an Ancient item when I can use in a LoN build.
I would like players to come up with an idea similar to LoN for Primal Ancient items that would make new item combinations GR80+ viable.
For example, think of a new set where you get a big bonus for each Primal Ancient item with a power for a different skill, and the set bonus requires your items to have powers for distinct skills. This could open up totally new build possibilities.