Regarding brutal critic of my suggestions

I agreed with big part of it but!
Vietnam (Dai Viet + Champa + Prey Nokor province of Khmer)
This I can get behind, but I suspect it's only because I don't know the history of the region at all. I really would like a more dynamic Vietnam region though, and that seems like a good way of achieving it.
On the other hand, it would be really really easy to achieve. I think we need more provinces there.
Christ, you could say the same thing about forming Ireland, Hannover, Westphalia, arguably also Scandinavia

(you basically need to beat one enemy country to form it)
I more care about Dai Viet vs Vietnam naming problem but while 'Great Viet' sounds better than 'South Vietnam' - hey, wasn't the first name also abandoned historically for the sake of 'Vietnam'?
Durrani Empire - essentially Afghanistan+ Pakistan + Nishapur, with capital in Afghanistan
Isn't Durrani already a country in the game? Why should it get a formable that does nothing more than append 'empire' to its name? If it isn't then yes I think it should be added.
No, Durrani isn't in game. At least it isn't on the wiki and I have never seen it
Great Mandala - modern: Burma, Thailand, Laos, Cambodia, Vietnam
Hmm. I guess at least it's better than the oft-suggested formable Southeast Asian state of 'Indochina'... The problem I often see with suggestions like this is why should there be a formable here? The cultures across this region are different cultures, they don't even group all that well (to my knowledge). It would be a bit like suggesting there should be a French/German/Italian formable uniting the three regions in one country. Stupid.
1) They have close history and strong cultural bonds.
2) They have their own characteristic features such as mandala government system.
3) They all are regarded as part of 'Greater India' (this is cultural term)
4) Few times in a history the majority of Indochina has been united for longed periods of time, especially notable being Taungu Empire and Khmer Empire.
5) One word my friend, just one word.
HINDUSTAN!!!
Maghreb - Morocco + Algier + Tunisia
Another one I just don't see the purpose for.
What is the purpose of Westphalia, Kurland, Hannover, Bukhara and Romania? There is no purpose - there is just flavor. Maghreb is separate unique region with Berber roots which was united for a long period of time by Almoravids and Moors, so this concept is not entirely ahistorical.
Kurdistan - possible to do in AOW map with expanded Caucasus
An interesting idea, but it would require creating at least one tag with primary culture Kurdish. That's something you should be considering when you come up with all these ideas - what requirements other than control of territory are there for creating them? Georgia or Aq Qoyunlu or Nogai or whoever forming Kurdistan would be retarded.
This area is going to have like 2x more provinces in AOW - and Kurds are not very small ethnicity. Hey, in modern times there are 30 000 000 Kurds in this region...
Axum Empire - Ethiopia + Adal + Eritrea
Ethiopia is already in the game.
Ethiopia is not the same thing as Axum.
http://en.wikipedia.org/wiki/Kingdom_of_Aksum
If this game already has such stuff as Mamluk Empire becoming Egyptian Empire in 16th century, 'Hindustan', 'Malaya', restoring Byzantine Empire and uniting Holy Roman Empire I don't understand why restoring glory to the name of Axum and uniting Ethiopia + Eritrea + Adal would be so bad idea
Somalia - Ajuraan + Adal
I don't really see the purpose of this. Replacing one tribal named state with another. Seems kinda pointless.
1) Open EU4 wiki
2) Check page 'Bukhara'
3) ...
4) See? Nobody cares
Missisipi - Native American Empire constisting of provinces of 9 tribes close to Missisipi River: Cree, Chocksaw, Cherokee, Osage, Caddo, Pawnee, Susquehannock, Miami. Capital in Cahokia.
I guess formables for native Americans would be cool but I really don't like it. Idk why. I think native Americans just need a lot of work to really differentiate them from Europeans. CoP did a crummy job of it, and weird ahistoric formables won't help.
1) There is absolutely no other option for any NA formable, unless you like 'Native Confederation' country

2) Cahokia being biggest pre - Colombian city in NA and the center of Mound Builders giant culture and a source of legends isnn't exactly more ahistorical than Hindustan
AND! I have forgotten about one particular possible formable. Of course it didn't exist in EU timeline in any way, but it is not much different from Romania, Greece, Malaya and Hindustan as it appeared historically later:
YUGOSLAVIA
Croatia, Bosnia, Serbia, Montenegro. Come on - Balkans already have limited gameplay and limited flavour, it would be so cool to have some goal here! Also, Yugoslavia would have it's own NIs so it would finally make sense to play as Croatia, Bosnia or Montenegro with their generic bad ideas being turned into Yugoslavian ones.
Also I would have nothing against
http://forum.paradoxplaza.com/forum/attachment.php?attachmentid=115349&d=1411131983
MYANMAR - Pegu + Taungu + Arakan + Ava + Hsenwi + Mon Yang cultural union
and as alternate option to Malaysia (if first exists, it makes creating second impossible)
NUSANTARA - basically Indonesia but possible to unite only by Majapahit, with capital in Java, separate events and NIs and based not on Malayan Sunni religion but on Javanese Hindu religion.
Nusantara is Indonesian term for archipelago, basically I'm talking about restored Majapahit Empire but Nusantara soudns so much better

Also this formable country would be kinda similar in its concept to Hindustan.
Also:
Australia
Philippines
Boer State
<if AOW is going to split Madagascar on few historical kingdoms> united
Madagascar (just like uniting Ireland)
Arabia
The Caliphate the country formed when a player achieve 'unite Islam' decision