I don't see it quite working out that way, but I do think you and I are pretty close to seeing the expansion playing out in similar ways.
I view it as Turalyon pushes the alliance towards embracing Yrel's Lightbound army, significantly causing a rift in the alliance, and some members of the alliance (especially Alleria and the Void Elves) being considered a threat due to their void connections. On the horde front, I can see Thrall almost immediately opposing Yrel because of the Mag'har, but that can cause strife in the Horde as well because of the new Forsaken leadership and maybe even some Sunwalkers and Blood Knights defecting. On the flip side of that though, Yrel's presence could kickstart a new crusade for the Scarlet Crusade and cause them to attack the Forsaken in Tirisfal Glades and Gilneas with Turalyon (and potentially Greymayne) pretty much looking the other way.
In the end, I believe Yrel is potentially a very destabilizing force for Azeroth. Thrall's role would be the stabilizing force, and a wonderful way to reinsert him as Warcraft's main protagonist for the 20th anniversary of WoW.