Finally cracked this whole deadeye thing.
- New champ is a darkin (Aatrox is the only darkin revealed out of 5 of them still alive).
- Varus and his bow are strongly related to the deadeye event
- That dark champ in the project video (the one Yi sees in his visions) looks pretty similar to this one: http://i.imgur.com/r5uB2HU.jpg - that's Aatrox, a darkin, you do the math
- Add this to the math on the previous bullet: http://imgur.com/a/c02bh - that's not Aatrox, just another darkin
- Ao-Shin is scheduled to be released somewhere in July 2016, unrelated to this new champ
- New champ unrelated to Shen rework
- New skins in the works: Star-Guardian Irelia, Arcade Diana
Disclaimer: I've gathered all this info from the web, I have no relation to anyone working at riot, don't even know anyone there. If anyone from riot curious to know where I got this just PM and I can share it, not that it does any good, the source is anonymous, just don't want to get into any trouble. This whole deadeye thing is driving me nuts but I love the detective work. :D
EDIT: forgot to mention the new champ is actually Raa'Tul but renamed to Deadeye ;) and this is Ao-Shin for those who haven't seen the concept 'till now: http://apollo-na-uploads.s3.amazonaws.com/1434426843/jbde6IQQpKL5LM.jpg - it's community made , not official but it does a good job of showing the concept.
EDIT 2: written over a year ago, http://boards.na.leagueoflegends.com/en/c/story-art/EookJA38-the-darkin-facts-myths-and-theories Varus's bow is a darkin similar to how Aatrox is actually the name of the sword not the champion himself.