In theory at least Ctrl-[ "is" Escape and is already universal. Reason: simultaneously pressing Ctrl is the ASCII -> ASCII mathematical transformation "subtract 0x40" for keys that represent a single ASCII character. So for example Ctrl-M is 0x4d - 0x40 = 0x0a. M is 0x4d ASCII and carriage return (aka '\r', aka Enter) is 0x0d ASCII. Ctrl-M is, or at least should be, universally the same as Enter. Similarly '[' is 0x5b in ASCII, so Ctrl-'[' is 0x1b in ASCII which is the ASCII code for, you guessed it I hope, Escape. Phew that was tough on a phone.