> In the end, I suspect that teaching all the backslash commands to do
> nothing after absorbing their arguments is likely to be the least messy
> way to tackle this, even if it makes for a rather bulky patch.
Perhaps, but just glancing at \connect makes me think that for some
commands (present or future) the number of args might depend on the value
of the first arg, and variable expansion-or-not, backtick execution-or-not
could alter the number of apparent args on the line, like this:
\set x 'arg1 arg2'