Well, given the covenant stories will likely be expanding on what we see in the different zones we can assume that:
Bastion will have ties to the Tyranny of the Light sotry that has been nunnling in the background.
Maldraxxus will have ties to the Kel'Thuzad return story.
Ardenweald will have most of the ties to BfA, with Bwonsamdi and Tyrande.
Revandreth will likely expand on the Denathrius/Nathrezim connection.