This is the most awesome E3 of the century. Why? Because lots of titles that I and most people like is having a long awaited sequel/remake. Doom 4 is a good example. Doom is my first PC game in Windows 95. That was like 20 years ago... Wow. Another great example is the full HD remake of Final Fantasy 7... finally! With these games (old and new) are now announced and in development, there's a chance that they will have a Play Arts Kai treatment too.
Now, for Play Arts Kai's significance in E3. I'm going to mention first some games that already have PAK figures that may have a chance on getting new ones because of their upcoming new game (sequel/remake). Again this is just my gut feeling and based on their older PAK/PA release, don't take the following info too seriously, OK?
Final Fantasy VII (Remake)
Chance: Sky High
Reasons: This is SQEX's pet title and FF7 have lots of classic Play Arts toys. They will make FF7 game version PAK figs for sure.
Final Fantasy XV
Chance: Already in development
Reasons: Noctis already have a prototype figure and I hope to see more characters being made as a PAK toy
Kingdom Hearts III
Chance: Sky High
Reasons: I saw a new outfit for Sora. Now what about Riku and Kairi? I'm also hoping for SQEX to make young Master Xehanort and Eraqus PAKs too.
Star Ocean 5
Reasons: The chance is low because I think the Star Ocean 4 classic Play Arts figures didn't sell well, not sure.
Rise of the Tomb Raider
Reasons: They made a PAK Lara Croft last time, why not make a new one based on the new game now?
Deus Ex: Mankind Divided
Reasons: SQEX made 3 PAK figures for Deus Ex: Human Revolution. If they're going to make a new one, I think they'll make Adam Jensen only.
Reasons: Like Lara Croft and Adam Jensen, Mr. 47 is already made as a PAK figure. This is my chance to pick this agent if they make a new PAK of him again.
Reasons: SQEX made a Nathan Drake figure and ignored Joel and Ellie from The Last of Us. This is why the chance for us to see a new Uncharted PAK figure is unpredictable just like the relationship between Naughty Dog and SQEX.
Assassins Creed: Syndicate
Chance: Low to 50-50
Reasons: I don't know if we will see new Assassin's Creed PAKs because the title is getting stale because of frequent new game releases in my opinion.
Reasons: I think SQEX love Halo. Did you see those Halo PAK figs, I'm sure you guys know that there are lots of 'em.
Street Fighter 5
Chance: Low to High
Reasons: SQEX made 8 SF4 figures plus 4 of the characters have a different color variation. Really hoping to see new SF5 PAK figures.
Metal Gear Solid 5: The Phantom Pain
Chance: Most figures are released now.
Reasons: Where's the young Psycho Mantis?
That's a long list, moving on... Here are some of the games in E3 2015 that may have PAK figs. Chances are pretty low though.
Final Fantasy XIV
Reasons: If my memory serves, Hidemi "Mad Dog" Matsuzuka of SQEX MD wanted to make FFXIV figs but I think they don't get that much demand on making them. Well, we'll see.
Reasons: It's a SQEX title and the characters are designed by Akihiko Yoshida (FFXII and FFXIV)
Gears of War 4
Reasons: This is the chance for SQEX to make them. The NECA Gears of War figures looks really good to look at. Imagine if they are PAK figures.
Well, that's about it. Like I said, this year's E3 is awesome and toy brands like Play Arts Kai, Neca, Figma etc. will also benefit on this event by making those figs that we saw on the game trailers.