The uncertainess of the Elemental and Shadow power source is my opinion based on what happened with the Ki power source and some very ambiguous comments about Elemental and Shadow. I could very well be wrong, its just my opinion that they are "in jeopardy" of being axed.
Ok, so entropic curse is out. It was only meant to apply ongoing damage during an encounter; (RP: it only hurts when you are directly channeling your powers) it was a long shot to begin with, but I wanted to see the reaction before I axed it.
I really liked the suggestion about turning the elemental brand into a power to make the wording easier. I struggled with how to convey how it worked and that is much, much easier. Also, to reduce confusion, it is now called
elemental scar. Not a huge difference, but hopefully less confusing.
In regards to the "rolling", in keeping in line with how the wild magic sorcerer works (as nifft pointed out) I think it functions as a unifying aspect of the Elemental classes. The idea is that the powers of the Elemental Chaos are not easily controlled. Using them necessarily forces a certain amount of variability and uncertainty into your character. Allowing you to simply pick a channel is too much of a boon, especially as the classes are currently written.
Imagine a creature that is vulnerable to your damage type. You automatically get extra damage on EVERY hit where you hit with your weapon and you could grant A LOT of extra damage with your Elemental Scar if you let another character use it for a different attack. Or if they have resistance/immunity, you are now completely hobbled.
I really like concept of the Wild Magic Sorcerer and wanted the Elemental classes to follow that same trend. There is a write-up of a class at 4shared.com that is more on the lines of being able to pick your element (
4shared.com - document sharing - download Elementalist.pdf), I think that's more the kind of experience that you're looking for. That being said there will be feats and paragon paths that allow you to stabilize this chaos and be more selective about your channel; e.g. Improved Arms - When you roll your channel of arms damage type you can choose from your dice result or the type one above or below your die result. I.e. you roll a 1, you can choose acid, cold or poison.
Perhaps, for the onmyoui and sentinel, rolling each round may be too much, but then they would need a feature like the geomancer to re-roll a set number of times during the encounter.
I really think that keeping the "randomness" is quintessential to the concept of the character. Thanks for the interest though, I hope you stay interested.