Trent 900 and GP
7000 engines on initial A380 production will be rated at 70k lbs which is one third less than the largest GE90 engines.
The A330 and the A380 have roughly the same engine thrust even if the 330 is way less than half as heavy. Twins need that extra thrust in order to survive an engine shut down after V1 speed during take off.
Using the GE90-115B the A380 could easily have been a three engined plane like the MD11.
It all leaves an interesting growth potential, maybe especially for the cargo market. Maybe allowable footprint on airport concrete will be the limiting factor rather than technical issues?