So this is a thorny yet very interesting topic.
Let me open by noting that we're going to get clobbered no matter how we handle this, just so you can get an idea where the thinking started. There are several mutually contradictory tensions at play here.
I'll start by laying out some truths as we understand them:
• There are concepts that are useful as building-pieces for a game, and there are concepts that are useful simply to have around as concepts. Take Golconda, in Vampire. They eventually went into Golconda, years into the game, but for a whole decade they never really needed to— it was a rich contribution to the game as a mechanics-free idea, an ideal for players and Storytellers to imagine and tell stories about and dream of, and for their characters to dream of. It was rare, and poorly understood, and you could tell lots of stories about characters trying to figure it out. Golconda was useful as an idea, moreso than as a concrete thing, because as a thing it was one thing, but as an idea it could mean and be many things to many people.
• The ten-dot scale is illusory and always has been. Considering the sheer depth of Essence dots 2-5, there just isn't enough material there to add five more discrete notches to the scale. As such, Essence 10 was always really more of an ideal, a talismanic stand-in for "unimaginable power." Essence 6 was a conceptual stand-in for "the land over the hill," the thing that you can imagine but not grasp—power beyond what you have now. Basically, imagining yourself, but an order of magnitude more badass! Essence 7-9 were a kind of conceptual dead zone, there just weren't that many real gradations along the line, at least not for Exalts. The scale was more workable for gods, because gods are simple things compared to an Exalted Charm set, without nearly as much depth, and it's a lot easier to understand the difference between an Essence 6 and Essence 8 god than it is between an Essence 6 and Essence 8 Larceny Charm.
And yes, I know we tried to put a 6-10 "meanings" scale in DotFA. Like I've said before, we took some magnificent stabs at doing the impossible back in the day, and carried it off pretty well in some cases; but at no point did I ever kid myself that the scale produced wasn't shaky as hell.
• Lots of ideas just don't scale when you stretch them that far, especially when the lower-echelon stuff ramps up so fast. By Essence 3, a Solar fighter can launch attacks that cannot be avoided by any means, dodge any attack no matter what, and land blows capable of extinguishing the immortal Essence of the titans that built the world. By Essence 6 he swings his sword and kills armies, and cleaves hurricanes in twain, and can land attacks that inflict infinite damage. Even in the arena of combat, escalation becomes problematic (and SUPER problematic for anyone having to fight someone rocking these inflated powers). In other categories, it gets even uglier; by Essence 3, a thief can steal anything flawlessly without chance of failure or being noticed. Where do you go up from that? How can you get even better? How can you get seven whole categories of better? Even if you move into crazy stuff like stealing souls or stealing everything in a whole city, that's only maybe three jumps up the ladder— that still leaves four to go. Again, the scale is illusory.
• There's a contradiction in expectations when it comes to high-Essence power. On the one hand, people love imagining their First Age prior incarnations as these absurd Dragonball Z continent-shattering ultragods. On the other hand, some of those guys are still around; and people want the mechanics to support them. The World of Darkness has a well known Elder Problem, wherein the ancients are so much stronger than you that you may as well just put away the dice and bend over when they show up because no head-on confrontation is possible— it's like an ant confronting a man. People don't really like that experience in Exalted, they do not come to Exalted to play an ant. But they want to imagine ancient elder entities in the game as men next to ants. This, by the way, is the point where we can't win.
• After some thought, we came to the understanding that men and ants aren't really necessary or desirable for our game, and that you don't need that dichotomy to still allow for jaw-dropping feats of amazing coolness to still exist (the Solar swordsman cleaving the top off a mountain and then surfing it down into the army of demons in the valley below, etc). To elaborate:
• We asked ourselves, "what can a Solar at Essence 8 or 9 or 10 do that a Solar at Essence 5 can't?" and really the ultimate answer was "nothing." This clarified a lot of things for us.
• We thought about what we'd want a fight between a circle of young Solars and Ma-Ha-Suchi to look like, and the answer was ultimately "brilliant high-energy kung fu fight," rather than something different. So we started wondering what, exactly, Ma-Ha-Suchi needs to be able to do that a really old, seasoned, experienced E5 Lunar couldn't do, and the answer again seemed to be "nothing, really."
• In fact, in all the casting about for stuff, we found very few effects that were to the game's benefit that didn't seem to be able to exist in the E1-5 range. We looked at elder Exalt after elder Exalt and asked, "what signature thing does this person have that sets them apart from others of their kind, that clearly emerges from their elder Essence rating?" and really the only thing that cropped up was Leviathan as Whalezilla.
• The Exalted system is an abstraction rather than a representation of how the setting works and how characters in the setting work. As a result, drawing the line up to the point where you become something all out of scope with your own nature and representing that as just more of the same stuff that represents the standard was……… not really smart.
What does this mean in terms of EX3's support for high Essence?
You can expect high Essence to still be a thing that exists. You can expect to eventually get stats for Mask of Winters & etc— you will be able to fight him and it will not be a 1e Kukla situation where it's like "turn in your character sheets." You can eventually expect to see Ma-Ha-Suchi and Leviathan and probably Kejak statted.
What you shouldn't expect is for us to jump right back into anything like Dreams of the First Age rules. You probably shouldn't expect the power curve to look the same. You shouldn't expect to load your character up on E6+ Charms— what ancient Exalts look like mechanically is still a matter under discussion and refinement, but at this point I really, really doubt they're represented by having E6+ Charms that cost 8xp each. And I am dead certain they're not going to be running around with Dex 10, Melee 10, because doing that melts the probability curves the system runs on all by itself.
That last statement is probably going to spark a shitstorm all by itself. Before you start shouting angrily, check this out. I am not discussing design philosophy there, I'm discussing math. If we give Kejak Dex 10, Martial Arts 10, it won't matter what Charms he does or doesn't have because your character cannot hit him— the odds of it happening are somewhere below 1%. That's a stupid place to start an epic kung fu fight from.