I erased some history a few months ago when a production password was accidentally committed to our repo. I totally agree that the need exists, but I'm not sure we need a new tool. git filter-branch worked perfectly.
Yes, master's SHA changed, but that's exactly what I would expect to happen! I'd hate for someone to be able to change my history without any hint whatsoever.
I do wish git handled rewritten remote branches better. When some people pulled, they ended up with a bizarre-looking merge, one branch of which I suppose had missing objects (I didn't look, just blew it away and checked out a fixed tracking branch). git should say, "hey dude, upstream has yanked the rug out. Maybe check your email for instructions?" and refuse to do anything until you've rebased things back to normal.