> The TeX engine should because of (old) plainTeX files, but LaTeX should use
 > \inputfile to implement its \input macro.

if one is actually seriously looking at base language changes one has to stop
worrying about compatibility at one point or one will have to deal with all
kind of special cases forever. and a new engine would probably be subtly
different anyway, so for processing old pain tex files one better use a real
TeX.

yes i can get rid of the old syntax by simply disabling the commands so from a
macro format point of you i don't care, but it it is not going to make the
internal engine cleaner if all that kind of stuff is carried along forever

frank