I've thought about this too, as it might be useful, but not sure how well it would work. Usually feature request voting lists are managed and features implemented by a single product owner, and used for prioritization. In this case, it would be open to anyone to implement posted ideas, and multiple people might spend effort working on the same thing. There wouldn't be a way to "claim" an idea to work on.
As such, it might be better just to keep it informal -- let people post ideas and requests to the existing forums, or directly to authors -- without trying to add a specific process to it. I'm not sure it would be worth the effort to build a custom Sencha version of UserVoice...