The proposed rule change makes good sense to me. With sector times getting longer and longer and flying over more remote parts of the Earth the weak link in the system is no longer the engines (allthough 4 still get my vote over two, all things being equal) but the other systems on the a/c with fire suppression at the top of the list.
Put a piece of string on a globe between Dubai and the West coast of the US and think about where you are going to go if you have a fire or cabin pressure problem. Looks pretty scary to me no matter how many engines are on the thing.
The other factor that needs to be looked at for high North and South polar routes is the facilities at the airfield for passengers. Little point in getting your 400+ pax. on the ground and evacuated safely if they all freeze to death 60 minutes later because there is nowhere for them to go. Depending on the weather you could be there for a long time, days, perhaps even a week or more.