Actually, there is already a standard way for someone to type these with the control key. To be specific, they are:

  FS: ^\ GS: ^] RS: ^^ US: ^_

Since these delimiters are not much used, on many terminals ^\ is mapped to send SIGQUIT. Use 'stty quit undef' and you can then type this at the keyboard. This works on Linux and OS X, and likely most other systems. Note that with most keyboards you are also using shift for RS and US. For emacs, prefix with C-q so that it inserts the literal.

Other posters have noted that they have ASCII separators recently, I have as recently as 2018 internally at a FAANG. So they are not completely unknown in the wild.

which modifier would that be, Alt/Ctrl or Cmd? Also there is a chance that this combo will not work on some platforms, some may already be in use as a hotkey.