There isn’t a whole lot of room between the crank and spokes; BB7’s are way too wide. Thinner mechanical calipers have been tried and they have all been found to be too wide for use with crank mounted or hub mounted discs on unicycles. See the first 3 pages of this thread for more: Disk Brake choice for new Nimbus hub
I tried a Tektro Aquila mech on a 26" uni with MountainUni disc setup, it was pretty close (another 2mm and I would’ve had it) but the clearance just wasn’t there. The Spirit crank arms look thicker than the Sinz to me (reducing clearance), though Spirit cranks have an additional 2mm of offset compared to Moments and Sinz so maybe the additional offset would cancel that out.
The only successful case I know of involved grinding down a no-name caliper for use with a square taper MountainUni disc setup on a 36: Mountainuni Disc Brakes Have Arrived!