Before you downvote this because 'aGHKOMKRito said no poakg new champs foar a whail ifze', Riot always has done kinda unexpectable things, not to mentoin the release date of Tahm Kench is almost a month ago and this is only the first teaser, and if I'm right and it's the champion it will probably be released after 3-4 patches, which will be another month waiting.
Now, this is the 'mark' or symbol which they used with the description 'They are coming':
As you can clearly see it has 2 lines: a black one and a white one, with each a curve in the middle. (The black one at the top side, the white one at the bottom side)
Now take a moment to look at this thread, posted 4 months ago:
And the reply of a Rioter, 3 months ago:
The champion is called 'Dha Ma' and represent Yin and Yang.
Now look at the back of Dha:
It has the same base design as the 'They are coming teaser'
But theres more. Take a look at this image of Dha Ma:
As you can clearly see they both have very curved tails, which is exactly what the 'They are coming' teaser has as well.
It's icon also looks familiar to the 'They are coming' icon:
Heres a comparison:
Dha is white, Ma is black. The icon also has 1 white line 'Dha' and one black line 'Ma'.
Both Dha and Ma have very curved tails, which the icon also represents. Their icons also look very familiar, as said already.
THEY are coming refers to more than one item, which in this case refers to Dha and Ma, as they're a dual champion.
Also, look at the description of the youtube video:
"Edit: No, its got nothing to do about the PROJECT skins."
Next, Wrekz, a champion designer at Riot, launched this tweet this morning:
One notable thing is that his last tweet goes back to August 15th about his champion Braum, indicating that hes really into this teaser. Confirmed it's about champions?
Then let's jump to storylines, Karma's one to be precise.
"To save her people, she drew upon the power within and summoned the full force of her will. A burst of spirit fire emerged from her body and spiraled towards the Noxian general. The flame took the form of twin dragons, the symbol of Ionia itself."
"Took the form of twin dragons, the symbol of Ionia itself."
Many players complained about the lack of Ionian storylines and champions, which could be another reason for Riot to create another Ionian champion. ^^
Before some players reply with 'It's not a new champion, because the icon is different' or 'It obviously has something to do with the void' etc, please keep in mind Riot NEVER copies fan-made champion concepts: they might change the name, the colors or even it's origins or the story line, but when I'm looking back at this thread I'm quite sure it's the first teaser for the new champion.
So it's PROBABLY a teaser for the new dual champion Dha Ma, but I'm not completely sure, of course it could be anything because it's Riot, but these are my thoughts.
What do you guys think? ^^
EDIT: Wrekz confirmed it's a champion.