The RB211-524H2 was only ever meant to be a stepping stone to the H3 engine. The H3 was to use the latest technology FADEC from the then new Trent series just coming online. However the H3 was a bridge too far in terms of meeting performance targets, and it ran too hot and fast. The final straw was an almighty bang on a H3 dev engine one nightshift in the Derby test beds, debris all over the test bed floor, and not long afterwards the H3 was canned, (along with similar developments of the 535 as well the E5/F5) So the 747-400 was stuck with the slightly older technology -524H2.
Very interesting times at RR, with the birth of the trents, V2500 and RB211 developments. There was a final development, with fitting the Trent 700 HP module, which actually gave a marked improvement of fuel burn and TGT.