Elemental Shamans are very good DPS.  But what if instead of going further down the elemental tree, you put your points in ancestral knowledge, enhancing totems, and mental quickness?  It may sound crazy.
Ancestral Knowledge-Increases your mana pool
Mental Quickness- Increases your spell damage by 30% of your attack power.  I am an elemental shaman (now this hybrid) with 326 attack power unbuffed.  This increases my spell damage by about 100.
Enhancing totems- Increases your strength of earth totem and windfury totem effects by 16%.  This is good, because if you put down strength of earth totem, you would normally get 172 attack power.  With this talent, it gives 199.52 extra attack power, or 59.896 extra spell damage.
You might ask, Isn't lightning overload better?  If a lightning bolt hits for 1k, then a lightning overload hits for 500.  It has a 20% chance to proc.  150 extra spell damage has an 100% chance to proc.  If Lightning overload procced 20% of the time, then in the same amount of casts, you would have added 750 spell damage with the hybrid tree.  750 is better than 500.

Post comments, I'm wondering if this kind of build could really work.

Enhancement shammy need different stats (str. agl. sta)then element shammy (sta. int. spi.), but they are close in DPS.  I would give an small edge to element shammy.  So in order to make a strong enhnacement shammy would be grap the wrong stats for strong elemental shammy.  Which would nerf ur DPS for both spec.  Another note is that weapon totem like Wind furry totem doesn't increase your DPS just your party DPS.  (Ur normal wind furry enchantment is already more powerful)  Yes u can improve str. and grace of air totem which help ur DPS (and everyone else in the party)

So to make long story short I don't think u could enhancement/ele hybrid to equal more DPS.  The stats don't merry up.  Almost full enhancement with 10-15 point in elemenatal can make for some add DPS.

Hope it helps good luck

Enhance are better no offense if you want to do damage. But if you ever change completely to enhance, dont cast but with the shock spells, and duel wield with axes or maces with a double Windfury.