DERG
Oil temperatures of 196C max are not acceptable in my view, but you must remember the Trents have three rotors and therefore more heat to disperse than GE products. Another issue that has been over looked is th the fact that the coking (tar like carbon) deposits are flammable.
I agree with you on the ever increasing oil temperatures. The tent is being moved closer to the edge of the cliff.
As things are moved closer together as is happening in the newer engine, heat dispersion is a problem, especially when a hot engine is shut down and the soak temperature rises higher than the maximum operating temperature of the oil. IMO, coking is still a problem and major concern even with the newer oils.