Hey,
nice to hear that you like our mod.
Just a few small marks:
1.) Edain is purely a third age mod. All factions follow a special timeline. Gondor, Rohan, Isengard and Mordor are around the war of the ring +- a few years, Ered Luin is set around 80 years earlier, when Smaug was killed and so on.
Especially in a faction, we want some "logic". Of course you will always be able to fight Gondor vs Gondor vs Rohan in a skirmish. But if you just look at Gondor, there are just heroes who lived at that exact time. There were no "grand grand grand grand grand fathers", who died before the other heroes were born. We don't want Isildur and Aragorn fight side by side in the same faction, as it would always seem not right.
Angmar and Arnor are also set in a very specific time window. Yes, Angmar and Arnor are many hundred years before the war of the ring, but it is still the third age AND looking at Angmar and Arnor on its own, the time window is really small.
2.) Other ages are really difficult to combine with the third age.
In the first age there were "normal" human beings, who crushed hundreds of trolls without any problems. The strength and balance of heroes and races would be completely off.
Imagine having a hero who killed hundreds of trolls on his own (and is just a human being) and right beside him you have Aragorn, the strongest hero of the war of the ring, who lead a whole army who died to... orcs. Oh, he also didn't manage to 1vs1 a troll...
I think you notice the problem.
3.) Every new faction needs a ton of work. Completely new units, buildings and heroes... Just having names is not enough. Getting names is the easy part, but creating models for them and designing their gameplay would get really hard. Of course we can just give them standard spells like "makes units stronger and heals them" or "makes units faster" or "deals damage", but if you compare it to our current factions, you might notice a difference in complexity. Those factions would actually be really boring and similar to Bfme II just copies of each other. Hence it would take a ton of time.
4.) There is a maximum of possible factions. We can just add 3 more AIs (2, if we subtract misty mountains). All additional factions willl not have an AI.
We won't stop anyone from doing it... but we sadly don't have time for that.(and our priorities are currently at other things like finishing 4.5 and afterwards adding misty mountains^^)