If you mean would the audiences of 2014 have accepted an evil Alex Moltke character, MB, I'm sure the answer would have been yes. I'm not so sure about the audiences of 1969 which presumably was when AM was thinking of returning to the series. That was the year when the Leviathan plot gave Frid the chance to play an evil, devious, scheming Barnabas again, and the fans revolted. The outcry was enough that the entire storyline was drastically curtailed, resulting in quite a hash, and the good heroic Barnabas quickly returned to the scene.
I wonder if there would have been a similar outcry if fans' beloved "Vicki" had shown up has some evil minx, vampiric or otherwise.
You may be right about the AM situation if it had played out in '69 with that period still being exactly as it was originally. Though the premise I'm trying to put forth with this topic is how would fans have reacted to a variety of situations on the show if during its original run there had been an Internet and things had worked back then the way they do today. As far as Leviathans goes, it might have prompted a different reaction if that had been the case because one of the biggest problems many fans had was how Barnabas changed so radically overnight without any warning. But if things operated back then as they do today in the world of soaps, chances are very good the audience would have been clued into the premise of Leviathans, the producers, writers, and actors would have given their take, and on numerous message boards and soap sites fans would have endlessly speculated just what it might turn out to be like - and all that taking place weeks before Leviathans actually began. Very little is left unspoiled these days - and spoiled weeks in advance. Which is one of the reasons I suspect that once it was somehow released publicly (because it inevitably would have been) that AM had been willing to return as a darker character but DC had turned her down, fans might have turned to some sort of Internet campaign to get DC to change his mind.
And as I indicated above, this topic isn't just to speculate on what might have happened in AM's case but to speculate on anything and everything that fans may have tried to persuade the show to do differently by starting Internet campaigns? So, what else comes to mind? I know other things do because just in the years this forum has been in existence numerous fans have written about the things they would have liked to have seen done differently.
Just as another example beyond AM, might Barnabas and Julia fans instituted a campaign to have Barnabas forget about Josette, forget about SYTs, and focus his attention on Julia? After all, there actually were numerous letters like that sent to the various daytime magazines' comments sections, so it's not hard at all to imagine that if there had been an Internet, those fans might have organized on the Internet...