I think Stratholme could very easily serve as a teaser for the Last Titan, like revealing that the Scourge are under new leadership, but I don't see it being
the link between Midnight and the Last Titan. I don't see a world where the reason we return to Northrend isn't because of either Iridikron resurfacing from his old lair or the titans returning (which we've been told is going to happen at least at some point in the expansion).
It feels certain to me that the Scourge will be used as a way to bring back in some aspects of Shadowlands without the extremely unpopular bits, so I think if they have a new leader they will be intimately tied to the Shadowlands. These are the options as I see it:
- Denathrius: the nathrezim are responsible for the creation of the Scourge in the first place, and Denathrius is by far the most popular Shadowlands character of any significance.
- Mawsworn loyalists: some remnant of the Jailer. I don't think there are any existing good candidates, so it would need to be a new character.
- The Primus: he can finally become the villain he was meant to be. He could have a mental break following from his time as the Runecarver, or something else causes him to turn on us.
- A new hidden Death figure: the Jailer 2.0.
- Kel'Thuzad: again.
Of those, Denathrius is the most likely and naturally has a link to Stratholme via the nathrezim, if that matters. Mawsworn loyalists are possible but potentially a terrible move -- visually interesting but shallow and likely to trigger Shadowlands vitriol. The Primus is a fun option but really unlikely because it would be a huge shift in his character; maybe he'll help us free the Scourge instead. Jailer 2.0 would be the Jailer 2.0, so obviously not happening. Kel'Thuzad is entirely possible, but I don't quite see a way for him to return in a form that would make sense as leader of the Scourge.
So I think if we do return to Stratholme in Midnight, it'll be to reveal to us that Denathrius and the nathrezim have taken control of the Scourge for some reason. We won't move on it right away, but it'll be important when we coincidentally find ourselves back in Northrend.