Since Echo3 has got it's cool side and Echo2 is still more stable and essentially a different set of components at the moment, wouldn't it be interesting to use Echo2/Echo3 side by side until Echo3 completely replaces Echo2 in all of its functionalities and component sets?
This could be a very smooth transition for any Echo2 based apps, and it could give Echo3 some early production tests. Unless, of course, Echo3 has already got all of Echo2 components ported. But I don't think that is the case right now, is it?
You already can use both
You already can use both frameworks, they have different classnames.
But they won't be "talking together" since the fundamental class and protocals have been completely reworked.
André