Please don't worry! SER / ER / ECoR will also soon shift towards 3-Phase Locos! Of course, the process will be slow. However, CR/WR/NR/SR/SCR are the first ones. It is surprising to see that ER / SER is as old as CR / WR / NR (in terms of electrification / electric loco shed, etc) and still, they are not moving towards three phase locos!