firstfloor
I agree with your post.
Fire - increasing temperature of IPT disc in the bore area - fracture of drive arm - increase of rotor speed - disc rupture - the end.
In the Trent 772 Edelweiss failure, a similar scenario: Fire - fracture of drive arm - disc does not rupture - the end.
The differences are: The IPT rotor in the Trent was probably turning at lower rpm's (7000 maximum permissible) verses the Trent 900 (8300 maximum permissible).
Temperature at the R850 holes in the Trent 700 disc arm reached 1832℉, a combination of friction and fire according to the NSTB report.
The first contact of the IPT rotor in the Trent 700 would have been at or near the tip of the turbine blades as they contacted the Stage 1 LPT nozzle slowing (breaking effect) the rotational speed of the disc. The Stage 1 LPT nozzle tilts forward at the OD. In my opinion, this feature saved the day in preventing increasing overspeed and disc burst.
The first contact of the IPT rotor in the Trent 900 would have been at the drive arm interface near to the engine centerline creating melting and potential further rotational speed, no breaking effect there. The Stage 1 LPT nozzle does not tilt forward and the airfoils are recessed because of a large forward ID overhang design.
Key factors: Hoop stress at the disc bore - radial stresses in the disc web - temperatures at the bore (keep less than ~500℉) - at the rim (keep less than ~900℉), both depending on the capability of the disc material.