"Nope, no can do. "." is used for ssyntax as well."
Even though . is used for ssyntax, .. isn't, at least in Arc 3.1. While (ssyntax 'a..b) returns t, ssexpanding anything with .. in it throws an error.
You've talked about classifying ssyntax as prefix, postfix, and infix before, so I suspect you'd want a..b to expand through (a .b) to (a (get b)). As for me, I think it's nicer to treat multiple-character sequences like .. as their own operators.
