Here's the thing, Maki shijo is part of a branch family which distanced itself because they disapprove of the Shinomiya family's methods. It wouldn't be a huge leap to presume Mikado is of a similar, critical mind. Maybe he'll be an ally in the end, Snape-style.
...
Or he'll pull a card from another of Allen Rickman's roles, ntr miyuki (wrecking Kaguya's mental state), and send miyuki on a musical, revenge-fueled murder spree, ala Sweeney Todd!
SWING YOUR RAZOR WIDE, MYU-KI!
HOLD IT TO THE SKIES!