I think they're mostly pretty obvious -- none of the following will ever be updated.
Just off the top of my head:
Variables (not including the 32-bit-only variables):
And, of course, any version of Take Command / TCC that runs on Windows 32-bit. (Version 21 will be x64 only.)
This doesn't include the commands that are still commonly used but actually call other commands (like REN and TITLE).