You can absolutely make a list like this and do well enough. I've faced 'Captain Planet' style lists in the past, it's a visually fun army with tools for different situations. Extra points if you can add in a greater for each element as well as the lessers
The downside is that the list threatens to end up fairly small and elite (and slow) if you take only elementals. Fudging in some woodland critters or similar chaff would be good for chaffing / objective work, but points eat up quick.
If it helps, here's a quick 2300 point list that takes all of the elementals, as well as the very sexy Wiltdaddy:
Forces of Nature
Earth Elementals (Horde) 220
Water Elementals (Horde) 220
Fire Elementals (Horde) 220
Air Elementals (Horde) 220
Forest Shamblers (Regiment) 120
Forest Shamblers (Regiment) 120
Greater Earth Elemental 230
Greater Water Elemental 180
Greater Air Elemental 180
Greater Fire Elemental 175
Tree Herder 260
- Healing Brew 5
- Upgrade to Wiltfather [1] 40
Forest Warden 90
- Inspiring Talisman 20
-------------------------
Total Unit Strength: 22
Total Units: 12
Target Points: 2300
So much variety! I'm a fan, and the list isn't that slow with the flyers and scouts and Sp7 water dudes.
EDIT: And here's a version that includes a couple non-elemental heroes, gaining more (and easier used) surges, a third inspiring bubble and some healing (especially when you include the Tree Herder's healing aura):
Forces of Nature
Water Elementals (Horde) 220
Earth Elementals (Horde) 220
Fire Elementals (Horde) 220
Air Elementals (Horde) 220
Forest Shamblers (Regiment) 120
Forest Shamblers (Regiment) 120
Greater Earth Elemental 230
Greater Water Elemental 180
Greater Air Elemental 180
Greater Fire Elemental 175
Tree Herder 260
- Healing Brew 5
Druid 65
- Surge (4) 10
Druid 65
- Surge (4) 10
-------------------------
Total Unit Strength: 21
Total Units: 13
Target Points: 2300