I would be so upset if we never got to hear English Es. Hopefully, if they do dub it, she won't be given a voice similarly to the Murakumo units. Definitely somewhat monotonous, but not 100% robotic is how I always perceived her voice.
Personally, I've always thought Christine Marie Cabanos would be a great choice for Es, especially if she did something similarly to her performance as Chiaki from Danganronpa 2.
Oh well, only time will tell!!