When developped, the "TA11" to be dubbed later A340 was presented to prospects with full engine commonality with A320 Series ... when built, the powerplants differed, but the sales pitch caught the attention of Asset Traders. An A340 NEO revival (GTF or Leap) is what you raise here ... ? The question boils down in essence to six counts :
1. quadri range vs ETOPS330 twin range
2. quadri take-off performance vs twin take-off performance
3. dry engine weight of NEO x 4 vs ditto of eg Trent XWB x 2
4. engine-induced drag of NEO x 4 vs ditto of eg Trent XWB x 2
5. fuel consumption of NEO x 4 vs ditto of eg Trent XWB x 2
6. engine maintenance & spares costs of NEO x 4 vs ditto of eg Trent XWB x 2
So to answer your question in some detail is not done in a snap of fingers ...