[RPG] GMless RPG with this structure?

I have never played an RPG, but I've been interested for a long time. In fact, I often say that my childhood play would've eventually led to my writing an RPG if I hadn't heard of existing RPGs first. The first RPG book I read was simulationist, and that's the direction my design tendencies would've gone anyway. More recently, I've wondered "Is there an RPG that plays like the one way I know how?" That is, is there anything that replicates the nature of my childhood non-game role-play, just with more rules?

The requirements:

• GMless.
  Specifically, there are no role distinctions between players, even temporary. Nothing like the rotating spotlight scenes of Polaris, Scarlet Wake or Archipelago. My play did sometimes have one informal shifting role – the player who railroaded the others who willingly went along – which I want to prevent. (More on this in a later point.)
• Multiple characters per player.
  Unlike many indie storygames, there isn't a tight focus on interaction between central characters. Okay, I may sometimes choose to play a story like that, I don't want it to be default/required. Supporting and guest characters should matter. In some rotating-spotlight games, minor characters are swapped around. In my play, even extras were owned by a player, and I want to maintain that. So I definitely don't want a storygame on the far end from conventional RPGs where no character is owned by anyone (I think Universalis falls under this).
• Narrativist.
  Our play was narrativist, if you categorized it in RPG terms. (EDIT: The important point I wanted to make was that we mainly perceived it in terms of "make a story about these characters" rather than "play as these characters". Rules mostly governed what players could control and establish as true, not what "actually" existed.) It was purely collaborative storytelling; gamist/competitive elements are undesired.
• Supports campaign play without character advancement.
  No fixed scenario playsets, "endgame" mechanics, etc. The latter should be self-explanatory… not that I expect a game like this to have advancement.

That's what's necessary just to replicate the style I know. There are a couple improvements I wanted to make a long time ago and probably wouldn't play without now:

• Mechanical support for keeping players on the same page.
  I fear unintentional humor or gonzo in GMless storygames. As a child, my tolerance for silly humor was much greater, and I only played with people I trusted to not break my extremely rubbery suspension of disbelief. I have much stricter requirements now. Something like Microscope's Palette would help here.
• Support for representation of in-world status of story elements.
  Things must have an in-game-world existence apart from the narration that describes them.
  Remember what I said about railroading? Though the Czege Principle was in effect in our play – solo role-play was inconceivable – a corollary wasn't. It was acceptable for one player to solve the problems he created. Over time, this in fact became the preferred option for at least three reasons. One, as we got older, our spontaneous creativity declined. So problems were created with a solution in mind, but you couldn't rely on another player finding it, so one of your characters had to. Second, almost all our rules concerned the players and what they could do. A lack of rules governing what could happen in the fictional world left no support for problem-solving. There was no rule for determining whether solutions could succeed, and the person considered best able to make the ruling was… the originator of the situation. Third, the "no competition" rule discouraged trying to resolve problems started by another player, as it could easily lead to trying to "top" their input. The result of these was increasing boredom.
  So, in short, the game needs a way to define task difficulties, or something equivalent, so my characters can gain traction on the fictional world. On a related note, I want stats for world elements other than characters simply because I don't want that laser-sharp focus on characters' internal states, particularly not in a game predominantly played in Author or Director Stance. (I was reminded of this by a comment I once saw about Burning Wheel, something like "there are no 'Large' armies".)

I haven't said anything about setting or genre yet, because I'm not sure a game that even fits this basic structure exists.
I have tried to write this game myself, but it's sufficiently far from anything I know that I can't.

(Here's hoping I correctly used the theoretical terminology and references to games I obviously haven't played.)

EDIT: Does the Mythic GM Emulator have anything that could facilitate this style of play?

EDIT Sep 28: Ideally, I want a not just a game that can be squeezed into this shape (even if Universalis or Microscope can), but a game where this is the assumed mode of play, RAW. I want to be able to say to other players, "I want to play _" and have them understand my goals and preferences by that.