"Who should be ashamed is your wife" is this ungrammatical? Why?

Is this usage common?

Example:

In your case, who should be ashamed is your wife.

I ask because 99% of the results in Google Books are "the one who should..." or "the person who should."

Maybe ...who should... is an incomplete phrase?

Solution 1:

This use of who (as a subject relative pronoun without an antecedent noun phrase) is almost obsolete. It was so used in older English, and survives in a few proverbs and quotations, such as:

Who steals my purse steals trash. (William Shakespeare, Othello)

But it is likely to confuse people if you use it today.

Edit: Oddly, what is still used in this way, eg

What annoys me is the traffic.

Solution 2:

You are right. Who does not work as the subject of a verb unless it is interrogative.

One can ask Who should be ashamed? Or who can be a relative pronoun, as in The person who should be ashamed is...

Even in informal conversation who always sounds a bit awkward as the subject of the verb, though it is sometimes used.