I guess the notion that "heathen" has been out of common use for a while, allows for easier re-definition. i.e. any connotations it may have/have had are not so fresh in the psyche.
This might just be me, but I have a much stronger averse reaction to the word heathen than I do to the word atheist. To me, a heathen incorporates visions of primitive people sacrificing virgins and dancing in the moonlight holding hearts over their heads.
Of course, I'm sort of contrary that way. I prefer to use the term atheist for myself just like I prefer to use the term liberal for myself. The opponents of both of these terms have done a great job of turning people against them. If I rebrand myself, I feel as if I'm letting "them" win and saying that my positions need to be tempered to fit into mixed company.
I'm a liberal atheist, and if you think that means I'm evil or something then that's your problem, not mine. (This is my thought for everyone, not specifically Heathen.)