> void f(auto x ...) // deprecated, equivalent to f(auto,...)

This is wrong. That case is not getting deprecated (and should not). I
have extended the deprecation example in the proposed wording, but I
think it's sufficiently clear otherwise.

Everything deprecated would become ill-formed in the future, or would
have its meaning altered by a future proposal that claims the syntax.
I don't think it's worth mentioning any of the cases that are already
ill-formed (such as (int......)).

I also want to keep what will become of the syntax intentionally
vague, since we don't know whether it will be removed or reclaimed.
All the developer needs to know is what is getting deprecated.