You should never use "What all".
You should never use "Where all".
You should never use "Who all"
You should avoid using never. And if you had read the previous 3 pages, you would have seen your own points countered.
They will think, "Is that proper usage? hmm...." and eventually make their decision. However, that doesn't change the fact that they thought it was strange to begin with.
You may think it's strange, but there are plenty of other native speakers, like me, that do not. Besides, you're wrong. While who is plural, it's requesting different information. If there is a party with 100 guests, and someone asks, "Who went to the party." then they are not asking for the names of all 100, they just want some highlights. If someone asks, "Who all went to the party." then they want to see the guest list.
Kinda like if you go to the southern states and you ask for a Coke.
What kind of Coke do you want?
A&W Cream soda is a pretty decent type of coke.