I don't think it would all make that much sense to change the name, that business would call them "that ex-metal band" then, the background stays there.
After all, Antimatter as a brand new band, were 'put' into the metal scene after the first release, right? ALL because of Dunc's past. Being on the bill between death metal bands and that... And Antimatter itself NEVER made anything that sounded slightly metal, still, you can find reviews of their albums in almost every metal magazine. So if we compare positions of Antimatter and Anathema, if Anathema changed its name, I think Antimatter had way better chances to approach a non-metal public, with its somewhat trip-hoppish sound and no direct background at all. It's the people in the band that count, not the name they're carrying, also for the music business. So in my opinion, Anathema would make a wrong decision if they change the name. It may be rather sad, but I think whatever band Duncan, or Danny, or Vinny is in, they would be linked to metal either way.