What new gifts could do, however, is give you a fallen aasimar with necrotic resistance or an ice tiefling or something or a dedicated half-aasimar half-tiefling, which seems more like what you're asking for in the first place. Also, I could've sworn there was a genasi somewhere in LU, but I can't find it anymore and it's definitely not under the planetouched heritage now, at least, so there's no reason to believe it would be lumped in with aasimar and tiefling (even though planetouched seems like a more appropriate umbrella for genasi than aasimar and tiefling).