The report comes from The Sun (insert grain of salt here), which quotes a source as saying, "The only stumbling block seems to be the number of films he is signing up for. There is a chance the character they want him to play could become a regular feature, like Blofeld back in the day." No other information about the character was given.
Whether or not the report is actually true, the idea of Hopkins playing a villain in a Bond movie (or any villain, really) is enough to get us excited. He knows how to make even the biggest of baddies charming (hello, 'Silence of the Lambs') and would be a perfect match for Daniel Craig's tough-guy persona.