The 34-year-old actor - known for playing companion Bill Potts opposite Peter Capaldi's incarnation of The Doctor in the BBC sci fi series - has said she feels a gender neutral Doctor is the natural next step.
Mackie told The Daily Telegraph: "I think it would be great to have someone non-binary playing the part.
"The Doctor doesn't really identify with human constraints at all. So I feel that could be a logical next step, wouldn't it?"
Jodie Whittaker, 39, made history as the first female Time Lord on the show in 2017. She confirmed in the summer that she is stepping down in 2022.
Mackie played student Bill Potts in the 10th series of Doctor Who in 2017 - and the actor is proud to have portrayed an openly gay companion to the Time Lord.
She said: "That's not something you ever imagine when you decide to be an actor: that you are going to help shape someone's life, or their journey, particularly something as complicated as nuanced as coming out."
But the 30-year-old openly gay actor and singer has played down the rumours.
The It's A Sin star and Years & Years frontman denied he is in talks to become the new Time Lord, but he paid tribute to the cult sci fi series in a pun-filled statement insisting he is focusing on his music career.
Watch: Matt Smith on returning to Doctor Who