The identifier method has a good deal of possibility also, basically it (potentially) becomes an efficient iterating method like $*. As long as it was able to be nested within other identifiers it could be very useful. Note that there's nothing preventing for from being both a statement and an identifier.
I wouldn't want to see the %var++/-- operators added though. While they serve a useful purpose in some languages where pre/post-increment/decrement are meaningful because variables may be set in-line, it doesn't make any sense in mIRC scripting where they'd have to be a separate command anyway. That is unless things like %++blah would start being valid expressions in commands, which I'd hate to see.