For a while now, adult animations have been able to use MFG morphs, basically custom face expressions that can be applied to AAF positions. Although, this was limited to only a single freeze-frame expression with no movement, which isn't very realistic. So, I've made a face animation system, allowing anything from a subtle face twitch to full cutscene-like animations. 

Each of the 54 face morphs have their own keyframe timeline, plus a 55th timeline for the eye position. Keyframes can specify any generic easing function from https://easings.net/, and I'm also looking into adding bezier curve easing for full control over keyframe interpolation.

This system is part of a larger framework I'm currently working on, which includes a scene system similar to AAF's made completely from scratch, but with many improvements made possible by leveraging the power of F4SE.