Iron-radio-group behaviour?

[rikbrowning]

Not an issue more a question/discussion point.
Very little of this element has to do with material design/paper elements. Is there a reason that it hasn't be put into the iron elements catalogue? That would allow people to use this with whatever radio buttons they want, currently they could but the semantics of the mark up would seem off by having a paper-element wrap around a non paper-element.