They aren't going to redesign the Mac mini again...
They wouldn't have to. I don't see a logicboard update (which is inevitable if going SB) being a redesign. If they can squeeze all of our wishlist into the current logicboard form factor, all that's preventing this from happening is whether or not Apple wants to do it.
All this would most likely come with a significant price increase so if Apple were to go with this, it would most likely be BTO. I doubt Apple would want another Cube-like flop.