I am not Phil but I happened to talk to Reef/Nauticam today. I was told that the new MIL viewfinder does not require a new LCD window to be used on the EM1 housing, but that the viewfinder does not mount very securely and "wobbles" when attached and at the moment, Reef is suggesting prospective purchasers consider using the DSLR viewfinder and the required replacement window instead. Going forward, the EM1 housings will have some sort of steel insert so the viewfinder mounts more securely, but at least for now, older housings are not going to be able to have the new design retrofitted.
I have concerns about whether the DSLR viewfinders will be usable on future MIL housings so I am going to wait a bit and let this situation sort itself out before I spend the cash. I am not going to be diving for a couple months anyway.
Hope that is helpful.