They haven't said specifically, but the early reports direct from RL state that ALL rigged bipeds will be able to be imported. The real question is "what does that mean". Right now, for example, you can import a Gen 8.1 figure into 3DX (and then into iClone). That, however, doesn't make it a CC character and there isn't any way to do that. What we would WANT is for any biped able to be imported into CC at the very least be "treated" as a CC figure in terms of being able to use CC clothing, hair and accessories. It's too much to expect morphs to work - those are very specific for a certain vertex count and orientation. But if we can at least leverage biped assets that can't be converted to the CC vertex counts/orientation we can do an awful lot with those characters.
Unfortunately, nothing we've seen from RL indicates if this will be the case. I think we'll just have to wait and see.
(Parenthetically - I am still hopeful that Gen 8.1 can be supported in CC3. And thus 4. The only real issue is texture mapping - it's NOT a vertex count issue. Thus the RL programmers ought to be able to fix this problem and I will continue to try and remind them of that).
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Mike "ex-genius" Kelley