If you eventually rebrand bitcoin it will create doubts in the minds of the persons we want to adopt bitcoin,after a good consensus,rebranding should be when we have the percentage of mass adopters that we think we need,but no need for rebranding, bitcoin has a good name ..
I think bitcoin doesn't need to be renamed, because bitcoin names and images as a tool to exchange and conduct transactions are good enough. Regarding negative images such as illegal, criminal, it's just a news issue highlighted to bring down bitcoin, because that's the other side of the negative campaign offered in countries that have rejected bitcoin.