Can nested structures be encoded more "readably" with a single delimiter?
\n and \t would get the job done as best as I could tell. In memory they're each only a character, but visually they offer a lot more. You then have an encoding scheme of \n then $x$ \t characters where $x$ is the nesting level. So this:

[a b [c d [e] f]]


in memory becomes:

a\nb\n\tc\n\td\n\t\te\n\tf


visually becomes:

a
b
    c
    d
        e
    f




As Evil mentions, you could similarly remove \n and \t between characters at the same level to achieve something like this:

ab
    cd
        e
    f