I'm thinking of this as the Forms system (forms as in the martial arts sense, not the wildshape sense).
Please note that this is intended to work with my Fatigue system rather than normal encounter/daily mechanics. Because of the awkwardness of keeping track of daily abilities when switching forms I think the reason for using Fatigue should be self-explanatory.
tl;dr of that mechanic is just that all your abilities are either at-will or encounter. Encounters are broken into 'tiring' (the old 'encounters') and 'exhausting' (the old 'dailies').
Core concept
Each class's abilities are broken up into Forms. A form is a list of abilities that a character learns over the course of five levels (with the exception of the first forms you learn, which you pick up a bit faster. More on that later). In combat, you choose a particular Form you are using. While in that Form, you have access to a particular set of at-wills and encounters. You can switch forms as a minor action, changing the set of at-wills and encounters you have access to. Each form also confers certain basic characteristics, gleaned from the class features of the class it derives from.
Nothing stops you from taking Forms from radically different classes, though given Forms do have prerequisites.
Form Structure
Forms are broken into five Masteries. Every time you gain a level in a Form, you gain a new mastery and therefore some new abilities in your form. You also have "passive" abilities which are always available. These typically mirror class features. There are 'levels' of forms, and you may not choose a form of higher level than you. Forms come in level 1, level 5, level 10, level 15, and so on.
Let's look at a sample level 1 form, the "Iron Wall Form".
Prerequisites: Proficient in shields.
Novice
Passive: While in this form, you may apply marks as a fighter and can use a fighter's Combat Challenge.
At-will: Tide of Iron
Encounter: Shield Bash
Able
Passive: You gain +1 to attack while wielding a one-handed weapon in which you are proficient and gain Combat Superiority.
At-will: One fighter at-will of your choice
Encounter: Comeback Strike
Adept
Encounter: Shielded Sides
Expert
Encounter: Shield Slam
Master
Encounters: Rhino Strike
breakdown
In most regards this just becomes a pretty standard levels1-3 shield fighter build. However, it changes at Master level where the player gets a level 3 encounter rather than a level 5 daily or the normal dead-level at level 4. Other builds, especially non-level 1 builds, might not follow the normal class levelup structure this closely. Also, a character at any level would have at least one other Form to switch to; a fighter might have another very complementary one-weapon-fighter Form and be able to switch easily, or might have, say, a Battlerager form in which s/he puts away the shield and goes bananas. At later levels a Sorceror might whip out a light shield and take up this form.
Finally, note that a character taking this as a multiclass Form would learn to be a fully classed fighter by Able level. Other forms might grant Tempest fighter-like abilities, or similar.
Finally, note that a character taking this as a multiclass Form would learn to be a fully classed fighter by Able level. Other forms might grant Tempest fighter-like abilities, or similar.
All in all, it is an unique idea for a classless system, both expanding and limiting at the same time. Setting up class feature 'packages', HP, defenses, BAB, etc. the same way, possibly using a point-buy system independent of the power system, can go a long way to making this a class-less system. A controller or striker could pickup a bunch of different implement features but take a major hit to HP, HS, and BAB. A defender could max out HP, BAB, and surges, pick out one package of features, or go the opposite, bulk up on saves and different marks and sack HP.
At-wills may need to be handled separately, as will utilities.
All in all, concept is great, not as swingy as most class-less systems I see. I'd love to see it come to fruition.
The point about level 30 is one I noticed myself. It's currently set up as-is so that level 1 characters get the full benefits of their class, functioning pretty similarly to current level 1s, but picking up new classes later gives you a limited form at first (ie. novice levels don't get all the class features at full power). That's just something I like for flavour though, mechanically it's not necessary.
Keeping Epic Destinies as-is would alleviate that for the most part, though: the epic destiny L30 capstones are usually amazing as they are. I've not yet considered how I want to handle EDs or PPs. I think the PPs would get integrated into 11th level forms (but that would take a lot of conversion bookkeeping unless done very flexibly), while the EDs would be independent of Form.... but I haven't worked that far enough to really consider the implications.