The way Mearls and others are talking, I think people are on the right track thinking that the class training feats are the new multiclassing. I think it was Podcast 20 where they said that what they had with multiclassing handled 'shallow' multiclassing well (ie dipping) but didn't enable 'deep' multiclassing... I'm still trying to figure out what they mean exactly by 'deep' and likely I won't know until I have the books.
My theory is that each class will have a class training feat tree. Feat number one gives you X array of class powers/abilities. Feat number 2 gives you THIS. Etcetera. There may be some ammount of choice in what you get, eg 'choose between x and y benefits from this feat', or feat branches that allow you to customize exactly what you get depending on how far up the core feat 'trunk' you are.
This gives you an in-built level limit in line with the availability of feats. And we've already seen feats that give access to powers (from the DDXP cleric). It could be that multiclass powers work much like the Divine Channeling feats from here: use x class daily/encounter power or y class training feat daily/encounter power but not both in the same day/encounter. Which leaves at-will powers just tacked on to your existing at-will powers.
Or, it could be more like wizard spell memorization. Choose between x class power or y class training feat power at the beginning of the day.
The good thing about doing it this way is scaling powers, retaining the usefulness of the feat at high level. Since it has been indicated that you will swap out old powers for better ones as they become available by level, there's no reason that you won't be able to do the same with powers gained from class training feats. Quite elegant, really.
My theory is that each class will have a class training feat tree. Feat number one gives you X array of class powers/abilities. Feat number 2 gives you THIS. Etcetera. There may be some ammount of choice in what you get, eg 'choose between x and y benefits from this feat', or feat branches that allow you to customize exactly what you get depending on how far up the core feat 'trunk' you are.
This gives you an in-built level limit in line with the availability of feats. And we've already seen feats that give access to powers (from the DDXP cleric). It could be that multiclass powers work much like the Divine Channeling feats from here: use x class daily/encounter power or y class training feat daily/encounter power but not both in the same day/encounter. Which leaves at-will powers just tacked on to your existing at-will powers.
Or, it could be more like wizard spell memorization. Choose between x class power or y class training feat power at the beginning of the day.
The good thing about doing it this way is scaling powers, retaining the usefulness of the feat at high level. Since it has been indicated that you will swap out old powers for better ones as they become available by level, there's no reason that you won't be able to do the same with powers gained from class training feats. Quite elegant, really.