While I think that the alliance should get something other than mecha gnomes, I don’t think it would be the devoted sethrak.
Also talking about what skeleton they use as base is not really relevant as blizzard said they will use whichever they think fit, and we already seen alliance skeletons on horde etc.
Now for the lore reasons why I think the devoted won’t join the alliance over the horde.
While the alliance does meet them and save the life of Vorrik, secure his keystone and break a faithless siege the horde does a lot more.
The horde also secure a keystone and save Vorrik’s life.
They then go on to reclaim ancient holy sethrak relics, go on the offensive against the faithless to even defeat the faithless leader Korthek with the help of the vulpera and Vorrik working together.
Sadly Mythrax is still revived (although he and Gh’uun will be slain later by the horde), and then the horde venture into the temple of Sethraliss and help her resurrection.
After all this is done we can even see two sethrak npcs appear in Dazar’Alor, one of them a priest of Sethraliss, which is also present during the coronation of Talanji. Showing that at least some Sethrak are starting to visit and making bonds with the Zandalari again since they’re ancient allies. Not to mention that Rakera, one of the two trolls aiding you through whole of Vol’dun is now on the Zanchuli Council. Rakera also seem to have been a bit influenced by the sethrak faith as she have literally said “Were it not for the mercy of Sethraliss, I doubt we would have made it out of Atul’Aman alive.”. This were before Sethraliss revival even.
Also in the new children’s week quest for the zandalari child, one is to go and meet the “sethrak queen” as the child heard tales of Sethrak that want to be friends and their loa that want peace. Which shows how the current relationship between the Zandalari and Devoted currently are in my opinion.