IMHO, at this point they should write off the ridges and make them all as smooth headed as the Vulcans. I forget exactly how long ago the Sundering was supposed to be, but having Vulcans and Romulans being almost exactly the same in appearance while having vastly different mindsets, seems like the way to go. They did it in the original series and in the new movie, and it makes the split between the two groups seem more like a family squabble as opposed to having two seperate species, which the ridges make you think is the case. It is something that can help bind them together closer, and make them seem like opposite sides of the same coin.