Uhm... let me recap what I think I've understood.
Background = the list of skills you (more likely) automatically have or (less likely) those you can pick
Theme = the list of feats you (less likely) automatically have or (more likely) those you can pick
The gaming group agrees whether you have to pick your background and themes and stick with it OR freely pick skills and feats.
There are different reasons why the DM would want you to stick with a background/theme instead of customizing: for myself, I can definitely imagine using a theme to represent membership in a restricted group, and therefore I see very good reasons to forbid cherrypicking from such theme (but in another campaign, the same could be definitely allowed).
At this point, backgrounds sound to me just like abolishing the concept of cross-class and restriced skills in 3ed, and just make every skill a class skill for every class. Then use the default class skill lists by class as examples of backgrounds (a beginner may prefer to do that, since it's quicker to pick skills from a short list instead of the whole list).
On the other hand, themes could be two things (and both could exist in the game): they could be just sample lists of core feats with a label (such as in 3ed, the "Archer Theme" = Point Blank Shot, Precise Shot, Rapid Shot, Shot on the Run...) to help beginners, but they could also be "containers" for non-core feats that are a bit stronger in flavor and perhaps even in power (think any Prestige Class's unique features to be broken down and turned into feats) in which case the Theme can be used by the DM to represent membership in a special group OR those feats can just be made available to everyone.
All in all I like these ideas, but they are not exactly "new"... quite a lot of people had such things as 3ed house rules!!
