This isn't "deprecate a few functions" -- it's basically an effort on par with migrating to Unicode in the first place.
I disagree you could just "easily" shove it into the "A" version of functions. Functions that accept UTF-8 could accept ASCII, but you can't just change the semantics of existing functions that emit text because it would blow up backwards compatibility. In a sense it is covariant but not contravariant.
And now, after you've gone through all of this effort: what was the actual payoff? And at what cost if maintaining compatibility with the other representations?
I disagree you could just "easily" shove it into the "A" version of functions. Functions that accept UTF-8 could accept ASCII, but you can't just change the semantics of existing functions that emit text because it would blow up backwards compatibility. In a sense it is covariant but not contravariant.
And now, after you've gone through all of this effort: what was the actual payoff? And at what cost if maintaining compatibility with the other representations?