Something that Itagaki himself would've objected too no doubt: "Itagaki creates his game characters by immersing himself in their roles and the games. This is a reason why he objects to the suggestion of Kasumi in the Ninja Gaiden universe, saying her 'soft' nature is conflicting with the 'hard-edged' nature of the game whereas Ayane perfectly fits in."
Which is why Ayane being playable should be a more regular thing honestly.
"We have choices. Some people like to stand in the rain without an umbrella. That's what it means to live free."