These were pulled and scrapped from the whole A380 fleet.
"Investigators also criticized the culture within the Hucknall facility that manufactured the HP/IP bearing hubs, identifying signs of complacency and widespread procedural non-compliance. A paperwork review showed that the required signatures were missing from 131 out of 138 retrospective concessions issued between 2009 and 2011, and a large number of minor non-conformances had not been properly handled through the normal chain of command."
> Within the space of four seconds, the energy from the annulus gas flow accelerated the IP turbine past its critical speed, until centrifugal forces exceeded the ultimate strength of the nickel alloy disk. The red-hot, wildly spinning disk instantly fractured into several sections, which rocketed outward in multiple directions at incomprehensible speed.
They got lucky.
TFA describes a fuel leak resulting from a piece of the turbine disk passing through a fuel tank located within the wing:
"When the fragments of the IP turbine disk passed through the wing and belly of the A380, they caused considerable secondary damage along the way, not only to the №2 engine but also to the left wing fuel tank, which sprang a leak"
It also includes a photo of the inside of the damaged wing tank.
Was the requirement you describe added after this incident?
It was a belt-and-braces fix, because the primary fix was of course to manufacture the engines correctly in the first place.
The "lots of temperature sensors" thing is actually easier said than done; jet engines already have lots of temperature sensors, and they will turn the engine off if a huge overtemperature is detected, but it's not a free win to add more of them. It increases the risk of a faulty sensor shutting down a perfectly good engine in flight, which from a safety-critical perspective is a borderline disaster condition all by itself.
(technically you usually cross-correlate temperature sensor readings with pressure sensor readings to prevent sensor faults turning engines off, but still, extra sensors isn't always a free win.)