Aight.
This theory bears several problems tho.
If the Primus was the big bad guy (i dont see this happening considering Denathrius and the Nathrezim. The rest of the Pantheon i can excuse because they frankly lack any sort of brain activity) and wanted access to Zereth Mortis then why use it to ressurect Galakrond? Galakrond was in the end nothing more but an oversized proto drake. And he literally died from choking. His enemies (pre buffed aspects, aka mere proto drakes) werent that noteworthy either. Same goes for Tyr (at this point all the keepers are cannon fodder)
So why waste time and effort on resurrecting him while you have access to Zereth Mortis and as such Azeroth. Giving you all the power in the world to unmake reality. He could just open the rift again if he pleased (after all it was his gadget that did it in the first place) and go nom nom nom on azeroth.
And it would be way too early. The forces of the Shadowlands are drained and exhausted. Revealing the cards (if there are any) that soon is a death sentence especially while that planet is infested with loot hungry parasites that would do unthinkable deeds if it means that it would upgrade their item level by just 1.