Let's see what we already have first:

Hammerfell - 5 - Stros M'Kai, Alik'r, sountern Bangkorai, Caglorn, Hew's Bane

Skyrim - 3 - Bleakrock, Eastmarch, The Rift;

Black Marsh - 2 - Shadowfen, Murkmire

Morrowind - 4 - Bal Foyen, Stonefalls, Deshaan, Vvardenfell

Akavir - 0 - (But this is another continent entirely, larger them tamriel)

Then look at some old, OLD maps...


...and start counting what's left to do.

Hammerfell - ca. 4-5 (Weeping desert, Sunforge, and depending on how they split the rest... two large or three small regions)
Western Skyrim - 6 (Falkreath, Whiterun, Pale, Hjaarlmarch, Solstheim, Reach)
Black Marsh - ca. 4-5 or so, depending on how they split it up...
Morrowind - 3-4 (Velothi Highlkands, Gorne, Telvanni peninnsula, either together with telvanni isles, or seperate for two regions)
Akavir - more then they ever could do for Tamriel
Imperial remnant - 3-4 (Colovia, Nibenay, Blackwood... they might split nibenay into valley and basin...)
Summerset - done
Valenwood - 1 (Falinesti)
High Rock - done
Elsweyr - 1-2 (from the looks of it the expansion will cover anequina and half of tenmar, so I assume they would split the rest in two DLC sized bites...)

I am hoping for more black marsh, since we have very little from that corner of tamriel yet. And they still should have some leftoverd from the first design of murkmire that they reworked in to what we got now. But... they DID recently do it with murkmire, so... perhaps skyrim or hammerfell might be more change of scenery?

Of course, the imperial connection with the elsweyr expansion might indicate that perhaps they could go there someday doon, see what tharns relatives have been up to... it was hinted at there will be more trouble from that direction, yes?

Akavir itself I don't see happening, but... there -are- three isles in the sea between akavir and tamriel, those would make an -excellent- expansion someday, with a story to find out the reason behind the invasion, and prevent the next one... while showcasing the akaviri... and perhaps even allowing players to enjoy them as crown store unlock race...

Whatever mainland zone not yet touched. I don't care what it is but some memorable creativity and uniquess, please.
Let the artists art and writers write instead of doing unpaid overtime applying formulas at assembly line.

Blacklight.