The dialogue for this quest is as follows:
Mizik the Haughty says: I'll take all of your anima!
Mizik the Haughty says: But... the Ancient One... promised...
Choofa says: It's done! It's done! Meet you outside the glen.
This is incredibly interesting to me, because the Ancient One is actually a creation of the Old Gods. The excerpt below is taken from the Wowpedia entry for The Ancient One. (Link to full page here.)
The Ancient One was an extremely powerful servant of the Old Gods that was vanquished long ago. It was the Old Gods' greatest creation and served as one of their many generals. Even long after its death, portions of the Ancient One's blood remains, and if enough of the fluid is brought back together, the being can be brought back to life.
Additionally, Mizik the Haughty drops [item=176730], and the flavor text on this states:
Sow havoc. Reap chaos. He will take his place as the one true God of Death.
The order itself says it is from (not about) The Ancient One. The phrase, "He will take his place as the one true God of Death," is a direct reference to Yogg-Saron. (As seen in the Wowpedia entry here, The God of Death is one of Yogg-Saron's titles.)
The involvement and mention of Yogg-Saron always brings up thoughts of the [item=64482], and whether or not it can be opened. I personally have always leaned towards the puzzle box being openable, but as with all secret-sounding things, there is a lot of uncertainty around it.
But at least two things ARE certain: old god corruption exists within Shadowlands, and Yogg-Saron is directly referenced as a part of it.