Anyway, I found some of this stuff pretty nifty and even mind-blowing, so I felt like sharing! However, I'm focusing on Symphonia since it's the Tales I've been tracking info for the most.

For starters, there was a Kratos-centric novel released late last year (images), and it's revealed a couple of new tidbits about Angelic skills:
Quote:
▪ It seems that the appearance of wings has to do with the individual’s mana control. Angels that have white feathered wings aren’t as skilled or powerful as the ones with pretty colored light wings.
▪ Kratos can control his body temperature and his sight/hearing enhancement at will.
(Source: x)
▪ Kratos can control his body temperature and his sight/hearing enhancement at will.
(Source: x)
(I think it's safe to assume that the second bit can also be said of the other most experienced Angels, Yuan and Mithos.)
Now, Takumi Miyajima, the scenario writer for ToS, stated in an interview (Source: x) that she originally had very different ideas for Dawn of the New World—she wanted the story of the game to take place 400 years later, and only Raine and Genis would be alive. However, the rest of the development team wanted to involve the rest of the original cast, which is why DotNW is the way it is today. (I feel like her original idea would be a pretty good base for an AU RP though... 8D)
She also has this to say about the different routes brought on by the affection system in the first game:
Quote:
I believe that every route is canon. The reason for that is what I talked about in last month’s issue: the route a player chooses is what is canon for them. That’s how I wanted it to be, and that feeling has not changed. And, if possible, I would like to ask this of all the players: even if the route you consider canon is different from another player’s route, please acknowledge that that player’s route is as valid as yours. Symphonia is a story where every possibility is allowed.
(Source: x)
(Source: x)
Now, that being said, here's this sequence of tidbits that I found breathtaking.
In the planning stage of ToS, the original idea was that Zelos would die in every other route where he didn't get the highest affection score.
That all changed when someone said, "Let's put Kratos in place of Zelos if we're going to make him leave the party."
I'm sure it'd be rather off-putting to paste a text wall here, so I'm just gonna say it's all expanded upon in this article.

Taking it a step further, there were even plans to continue the route where Zelos died in DotNW, but they weren't pushed through. However, the data for the skits unique to that route remained in the game and could only be revealed through hacking. Apparently, they were also even fully voiced.
In short, the route where Zelos dies almost became a solidly official thing. D: (Its exclusion from DotNW implies that "nah, that didn't really happen".)
Lastly, I leave this piece of info because I remember the subject being brought up in a thread but I don't remember when and where.

Quote:
Fujishima (ToS's character designer) asked if “The worlds in the Tales series were the same.” Yoshizumi (ToS's producer) responded, “No, that’s only the case for Destiny and Destiny 2 and Symphonia and Phantasia."
(Source: x)
(Source: x)
That's all I could think of sharing for now...actually, there was kind of a lot more I felt like bringing out, but I didn't know where to begin.

You can find a lot of translated material for the other Tales on this Tumblr, and you're welcome to sift through the stuff and comment on your findings out here even if it doesn't relate to my post XD.