While the dominion is strong i think the Empire is the best bet for Tamriel due to it's popularity.
I can't remember who it was who brought up the idea of redguards, orcs and nords vs the dominion but that would be something to see.
I wish that were true still.
The Empire isn't the best bet anymore, it's politicians are corrupt with funds from the Aldmeri Dominion, they hire Assassins to further their own gains; the basis of the Empire has been dwindled into a Sandbox where the kids are fighting over the shovels and buckets.
The best bet for all of Tamriel, is not only new leadership in each of the Races homelands; but a unified opposition to the Aldmeri Dominion.
An all out offensive strike on the Summerset Isles, to behead the best is really the only way Tamriel will not fall under full control of the Aldmeri Dominion.
The Nords and Redguards would, and could hold their own against the Thalmor and Aldmeri Dominion quite easily.
In Hammerfell, if you listen to the Alik'r, and read some of the Books, Hammerfell is no longer part of the Empire due to the refusal of bending knee to the Aldmeri Dominion, and the constant attacks and opposition to their rule.
The Empire has no footing in Hammerfell anymore, and it's just the Aldmeri Dominion trying to pry for a piece of control, which they're losing. It's why they want this Rebellion in Skyrim quelled.
If they control Skyrim, they will now have Imperial backing, as well as an alternate route right into Hammerfell, the "Sandwich" tactic if you will, would allow the Aldmeri Dominion and the Empire to squish Hammerfell into a centralized location, destroying the landscape, killing all who oppose them; and giving full control to the Aldmeri Dominion.
But, if Skyrim gains it's Independence, they will have new Allies to fight against the Thalmor and Aldmeri Dominion; along with the Orc strongholds who despise the Thalmor for everything they stand for; they would create a very strong opposition, maybe even enough to make the Empire itself renounce the White-Gold Concordat, and if they did that, and if they started engaging the Aldmeri Dominion, then just maybe the three would re-join the Empire.
Yet as I stated before, the Imperial diplomats are heavily enjoying the gold flow.
EDIT: It was me who first stated the Orcs, Nords, and Redguards.