Firstly, just going to say what has been said by Blizzard people multiple times: There aren't going to any great lengths with Allied Races to balance which get what classes for fairness sake. They are simply giving them the classes they feel make sense from a race perspective. That's it.
With that said, overall, things have been more or less pretty fairly balanced with regards to allied race/class combinations and numbers. Here is the breakdown:
Alliance:
Void Elf - 7
Lightforged - 5
Dark Iron - 8
Kul Tiran - 8
Mechagnome - 7
Horde:
Nightborne - 7
Highmountain - 5
Maghar - 7
Zandalari - 8
Vulpera - 8
Pretty much equal across the board. Mag'har got one less than Dark Iron and Vulpera got one more than Mechangnome. But, i mean... seriously? Who cares? Why is this so important? I mean, I suppose if you wanted to be annoyed by anything, be annoyed that Alliance Allied races only got two Paladins & two Shaman, while the horde got an extra Druid, and FOUR Shaman. But, yet... only one Paladin.
There is always going to be some kind of disparity. If they made it completely equal, how boring that would be?
That won't happen. They aren't going to get a special class specific to them. Why would they be vastly different from standard Gnomes? The classes remaining are:
- Death Knight
- Demon Hunter
- Druid
- Paladin
- Shaman
It's pretty obvious why they cannot be any of these classes. With the exception of DK, which A.) Blizzard said no Allied Races would be DKs as an option and B.) They would have been normal humanoid Gnomes at the time of the events of Wrath of the Lich King.
Gnomes don't have a connection to being a Paladin (Light), Druid (Nature) or Shaman (Elements). It's just not a part of who they are. Lorewise, the "Priest" gnomes use technology to heal, or learned from being with Dwarves. But they don't have the faith based beliefs to be the others.
Dunno what else to tell you here.