As they are already many legato combo in BBO, I'm a bit skeptical in what a Legato Performance Combos can bring new in the table.
I think child choir could be a nice contribution in the collection, as I suggested in Ganymede, a patch "short with random syllable" would be really awesome.
And the cherry on the cake, like some said, a pack with all "big scores" missing instruments (Harp, Sax, etc. and maybe some original like an electric guitar)