I think that some faction abilities could go be used as themes (others can simply be Boons as described in DMG2), similar to this. As I certainly see some faction abilities as an extra encounter ability. Though I'd have to find out more about how DS 4e handles things.
I think of the boons as described in dmg2 is a very good option.
I don't know very well the dark sun themes mechanics to say if it is good. Are they utilities or attacks?
So Dark Sun has "Themes" for characters which give them an extra Encounter Power at 1st level. The Themes in Dark Sun are things such as Veiled Alliance, Templar, Gladiator, Elemental Priest, and Wilder (as in the 3.5e Psionic Class). Defiling is incidentally an ability that all Arcane characters can get.
I think that some faction abilities could go be used as themes (others can simply be Boons as described in DMG2), similar to this. As I certainly see some faction abilities as an extra encounter ability. Though I'd have to find out more about how DS 4e handles things.