I finally did more testing of Echo of Elements. Wow Beta build is 15589. I used lvl 85 tauren Shaman. Testing specs were enhancement and restoration. That is important, because proc chance of this talent depends on your specialization. Damage spells were tested on lvl 85 Training Dummies (with one exception) and healing spells were tested mainly on myself and in one case on random afk hunter (lvl85)
I was wondering whether blizzard changed if certain spells can proc this talent and I found that Unleash Frost, Lightning Shield (static shock), Searing Bolt, Flametongue weapon proc and Frostbrand weapon proc can't be duplicated in enhancement spec. In restoration spec I couldn't duplicate Lava Burst, Unleash Flame and Unleash Life (didn't tried others), but that could by issue of very low proc chance. I don't know if its intentional or not, nevertheless it will be reported on the beta bug forum.
Now to the data. To determine proc chance I was using mainly Lightning Bolt (no cd, cheap, no dot), but proc chances of other spells were tested as well.
Enhancement spec:
Lightning Bolt: 76 procs out of 300 casts (25% proc chance)
Lava Burst: 24 procs out of 75 casts (32% proc chance) - lava burst now has 100% crit chance even without flame shock on target in enha spec (normal behaviour in resto spec). Great fun insta killing mobs in Twilight Highlands. Reported as a bug.
Chain Lightning: I tested this spell on one, two and three targets and results are at least interesting.
1 target: 9 procs out of 30 casts (30%)
2 targets: 22 procs (2 hits) out of 30 casts (73%) - note: only 2 available training dummies are lvl 80 dummies in Thunder Bluff.
3 targets: 17 procs (3 hits) out of 45 casts (38%) and 10 procs (2 hits only) out of 45 casts (22%) - 60% proc chance combined
Different proc chance on 2 targets and three targets might be result of small test sample, but it could indicate that proc chance depends on level of target. I need to do more tests on this.
Healing Surge: 6 procs out of 25 (24%)
Chain Heal: 9 procs out of 25 (36%) - only one torget.
Proc frequency of other tested spells was roughly same.
Restoration spec:
Lightning Bolt: 9 procs out of 100 (9%)
Greater Healing Wave: 7 procs out of 100 (7%) - partly tested on random afk hunter
Healing Surge: 9 procs out of 100 (9%)
There is significant difference in proc chance between two specializations. Enhancement echo of elements duplicates damage and healing spells roughly three times frequently than in restoration spec. I can't determine proc chance in elemental spec, because respecing is not implemented yet and elemental mastery also adds another dimension to this problem.
If you are interested in the raw data, you can find them
here.