Yet another SFA lossage

[KMP at MIT-MC (Kent M. Pitman)]

(RUBOUT ...) when TYO is set to an SFA loses. This isn't fair since
[1] My SFA supports CURSORPOS
[2] My SFA would say that it is a TTY output file if Lisp would
    look at what's in (STATUS FILEM)
The error message complains it isn't a TTY output channel.
(CURSORPOS 'X TYO) under the same circumstances wins, so why doesn't
rubout? I'd be willing even to make a rubout OP for my SFA-HANDLER ...