Re: Non X-characters
You could, sure. My assumption by wanting a Utopia-centered game was that you'd want it to be X-focused to the exclusion of all else. I like the idea of setting it post-Second Coming (maybe even post-Necrosha, which I think was after Second Coming right?) to get reactivated mutants (and maybe some revived dead mutants like how Cypher is now).
Smallville is the only one that really uses the relationship maps.
Serenity uses some stress tracks/knockout mechanics that are different, like a combo between Cortex Classic and Cortex Plus.
Cortex Classic is a more standard game, where you don't have the option to make Assets, Distinctions and such things in the narrative manner. It's a 'make pools and total numbers' and success is more like Unisystem, a bit.
Hence why I suggested Leverage.
@Social-Diseases
You mean an X-Men game set in Utopia, don't you? 
Single-sphere supers games seem to be about as rare, and hard to get people for, as single-sphere WoD games. Unless your genre is made to only be mutants, like the movie-based games... people will expect to be able to somehow make any other marvel hero fit into San Francisco and the Utopia focus.
Also, what kind of focus would you WANT from the game? Mutant terrorism and anti-terrorism? Internal friction leading to the X-Men schism?
@Lithium
It also feels like you're trying to articulate the issues with sandboxy ALL THE THINGS games, versus a single sphere game where it's easier to create focused plotlines as well? Which I totally agree on.
Hell, you could use the Flashback mechanic as Technobabble mechanic. All it does is set up the use of Assets (things around you that help your roll), so...
@RnMissionRun
Do note that each game does it differently ever so slightly, and each 'version' is titled differently in the Cortex Hacker's Guide. Firefly used Attributes and Skills; Leverage used Attributes and Roles and had a funky Flashback mechanic with their Plot Points. Marvel Heroic changes out Attributes for Affiliations (Solo, Buddy, Team) and Power Sets with SFX and Distinctions. And Smallville uses Virtues and Power Sets with SFX and Distinctions, and relies a GREAT DEAL on building a Relationship Map of who knows who, what, where, etc.
The easiest one ot hack would be Leverage (you could switch things to Star Trek roles) or Cortex Classic (which is used in Supernatural and Battlestar Galactica). I like the Cortex games but they can be VERY whiffy at times, depending on what you are doing.
So Storyteller's Vault has released.
This is WW's OGL setup.
www.storytellersvault.com
It allows you to publish your own material as PDF and sell it, using WW art, resources, etc. They have templates and such. Kinda interesting. You get a 50% royalty cut of every sale (standard in this type of thing).
@Catsmeow
Most of my friend who have done it have gotten cute messages or things like 'I've secretly been in love with you'. A couple of messages have been bad or insulting, but like all things, it depends on the people who have access to your sarahah. I haven't signed up personally, but they seem to have fun with it.
@Catsmeow
You sign up.
People can send you anonymous messages through the sarahah interface.
That's pretty much it.
Cortex Plus, with some hacked Stress Tracks.
@Seraphim73
I guess I'm the odd man out in that I LOVE doing planning RP sessions.
@Jennkryst
I dunno, I really enjoy the whole 'oh, you fucker, I haven't seen you since the French Revolution. I was sure that your head was ash in a basket!' But I come from an interconnected LARP background where that's a common thing that goes on, so I'm predisposed towards it.
@surreality
That's one of the things that I found intriguing about the Leverage RPG, is that you use flashbacks as an in-game resource. I like your idea of 'using flashbacks to integrate new characters,' as well.
@Thenomain
Heh. Seriously though, you get some inbuilt conflict and a reason for PvP. Ignoring the WoD fansplat for it, the TV series and first movie make a solid background (and just ignore the SPESS ALIUMS origin from the second and third movies).