I actually understand most of the allied races and accept them.
Dark Iron - Quite obvious but I look forward to where they will come from and what politics changes to let them be playable.
Zand - Rather obvious considering the expansion.
Shal'dorei - These have always been more closely tied to the Blood Elves than Night Elves. Elisande notes this, Tyrande is clearly not as enthisastic about helping them as Liadrin is from their quest text and Silgryn talks with Liadrin aboard the Vindicaar about the Horde. This is a broken race and they need allies. One faction may force them to chose.
Highmountain - I find these more unlikely than Shal'dorei tbh. Obviously they aren't Alliance, but Highmountain has no faction storyline in it (unlike Suramar). However, Baine is a good spokesman for the Tauren and I can see him progressing as a character because him and Mayla are quite similar (both young new rulers) and might even see tauren babies in the future.
Lightforged - No brainer for me. Defeat the Legion, what are all of these Naaru empowered Draenei meant to do? Follow their Prophet.
Void Elves - For me, the question is why not High Elves. Out of all of them, I understand these the least but, I accept they exist and clearly would not join the Horde.
I have no plans to play allied races, but one thing I wanted from this expansion was more race specific storylines. They may not be orders, but every race has the potential to create some progress in stagnant existing races storylines. The ones I most look forward to are dwarves and tauren myself.