It's important to note that the Revenant Genasi feat "Past Soul" does NOT give you the manifestation, only the power.

That's important, because Genasi have several feats that make them incredibly powerful, most prominently Shocking Flame, which gives Genasi the potential to add lightning damage or fire damage to all attacks at level 11 (with the appropriate soul) and both in Epic. Past Soul doesn't give the manifestation, so Shocking Flame doesn't work with it.