So, I'll admit that the Legendary quality looked really broken to me when I first saw it. I'll also admit up-front that I'm biased towards it, since I'll be able to take it as soon as I save up the 100 Karma.
That said, I'd like to bring up a few points about it. Our game is already going to be separated into tiers because there are people who are starting new and other people who have hundreds of Karma built up. Using the Legendary quality would draw another line, demarking a third, higher tier. I would argue that that line exists whether we draw it or not, but either way, it would either draw the lane, or make it a lot less fuzzy. I can see solid points both for and against it, and we can crunch numbers and talk about it all day, but I think we'd mostly be dancing around the real issue.
The simple fact is that we all want this game to last, right? We all are working towards, and can reasonably expect to succeed at, (re)building a lasting, successful campaign. So, in light of that, let's work under the assumption that, sooner or later, Gideon and Station are going to get the 100 karma needed to pay for that. The question is, what do you want the state of the game to look like when that happens? The way I see it, there are two options:
1) We use the Legendary rule. In this version, over the course of gaining the next 100 Karma, Station and Gideon pick up the occasional new skill maybe, but mostly do not advance otherwise, stockpiling Karma for the huge buy-in for Legendary status. After 100 Karma, there are two legendary characters. Station will basically literally never fail at anything he rolls dice on, racking up 15 or 20 hits on social rolls and throwing Edge at anything else that matters. Gideon will truly be the world's greatest generalist, being able to reliably roll three hits any skill in the game and more on the things he's particularly good at. Slide will be gearing up to start banking his own Karma (or already banking) to get Legendary after the next 100, and the new people will now be characters with 100+ Karma built up and spent on improving their characters while the very top-end guys were staying the same.
2) We do not use the Legendary rule. In this version, over the course of the next 100 Karma, Station and Gideon keep building up as they have been. Station, barring the occasional picking up of a new skill that makes sense in-story, continues running the Magic-Initiation treadmill. Having already picked up all the metamagics he likely ever will, he gets a new power point worth of Adept powers for each initiation. With 100 Karma spent on it, he will be a 6/6 Mystic Adept and Grade 12 Initiate. Gideon continues building the perfect generalist. Soon, he will be trained in every skill in the game (if he isn't already). After 100 Karma, he will have been able to boost a significant number of them to rating 2 or 3 and specialize in any he cares to, and could easily initiate a few times if he feels his magic powers need a boost. Alternately, he considers 1 in every skill sufficient and begins the Magic/Initiation treadmill. Slide and Mitori are reaching the caps for the skills and attributes relevant to their roles on the team and begin looking to branch out into other roles. The new people will now be veterans with 100+ Karma built up and spent on improving their characters, and are now much more well-rounded established and therefore less worried about the old guard stepping on their toes and muscling into their niche.
I may be overlooking some aspects here, but that's what I expect will happen, or something very close to it. The question before us is this: which of the two do we want to happen? As I said, I'm more on the side of allowing, so that way my bias lies. I tried to be fair in my presentation of both sides, but feel free to call me out if you feel I wasn't.
Note: I deliberately didn't add a poll because I feel that we should take some time going over it and making sure we aren't overlooking something. Introducing this could have a host of unintended consequences, and I'd rather no one feel blinsided by it.