I was recently discussing this exact topic with someone from this board (by IM). For me, on the most appealing aspects of the rape fantasy is that the victim does NOT want it. Therefore, I can understand the desire to want to go beyond the originally set boundaries, to the point where she no longer wants what is happening to her. As a safeword serves to protect the roleplay victim from exactly that, it seems that such edge play would require getting rid of it.
Of course, that sounds terribly dangerous (although exciting) to me. Can't say I'd endorse it, but would love to hear how it goes
