I think that Themes, as simply pre-gen lists of feats, are really lame. They're just going to end up being a trap option in any game that permits hand-picking feats.
What I'd like to see is a slight tweak, to give the Themes a bit of a boost, and make them viable options in and of themselves.
We've already been told that Themes will span 5 levels. You take one at level 1, than another at level 6. Supposing we get 1 feat per level, each theme would have those 5, plus 2 more. These bonus feats would be applied at level 2 and level 5 of the Theme progression. This gives the Theme some real substance, not just dev-recommended feat least.
When customizing feats, those Theme feats can still produce those bonuses. Basically, the 7 feats in the Theme would produce a "feat set". Take 2 of those feats (any of them), get a third free. Take 3 more of them, and get that seventh free. This gives Theme a real mechanical meaning, and should provide interesting choices between sticking with the thematically-related feats (at least to some degree), and mixing-matching freely.
Sigh. This makes me sad. I love the idea of themes, hate feats, and really wish I could get one without the other.
Even setting aside my problems with the feat system as it stands, I think it's a mistake to break themes into interchangeable feats. It's like classic 4E where they tried to cram every class into the AEDU model. The designers should have freedom to build each theme as a unified whole, without having to worry about what happens if someone goes cherry-picking a bit from Theme X and a bit from Theme Y.
I would prefer a system where you can choose either to take a theme, or to pick feats. Maybe some themes would have "feat slots" at certain levels, with recommended picks, but it would not be inherent to themes.
Even though I really like 4E, and feats, I like this solution even better than the one I described above. There's really no reason why Themes have to be entirely composed of feats. Just make them do things similar to what feats do, but as a cohesive whole.