[Image examples will be added in a future reply] While the elbow avoidance feature is great, on some avatars, it can sometimes be too much to the point where the elbows will start to point outward at any position or rotation the hands/controllers are in, resulting in a kind of "chicken dance" pose when the hands are rested at their side near the chest. In the old IK system, wrist rotation had almost direct influence on the position of the elbows relative to the hands actual position. This wrist rotation influence seems to have been reduced drastically in order to prevent elbows from clipping into the chest area. While achieving its goal, it creates an issue where the user seems to have zero control over where their elbows are going without elbow trackers. This is especially apparent when a user lays down on their side with their hands resting near the head or chest, resulting in the elbows bending upwards unnaturally and hanging into the air. Another instance would be when a user is laying down on their front side with their hands out to the sides pushing on to the ground, as if doing a "push-up". The elbows would unnaturally bend outwards, perpendicular to the body, where wrist rotation would not influence where the elbows would move, even if in reality certain wrist angles would make some of these poses possible. For elbow IK, A hybrid of the legacy system and the beta system could prove useful, especially with avatars of different proportions. Some characters chests/arms are so small it was impossible to have elbows clip through the chest, while other avatars had very long arms or wide chests and still clip even with the current changes. Having no control over the elbow movement without elbow trackers makes it difficult for those who are in strangely ill fitted proportioned avatars to pose naturally. As stated before, the legacy system allowed for quite a bit of influence of wrist rotation to influence elbow positioning, which could be used to mitigate these problems. This no longer possible with the little amount of influence now that wrist rotation has. Combining the two systems, either through a slider or hardcoded numbers, could give the best of both worlds and allow users to make adjustments if needed based on an avatar they choose. Elbow IK is extremely important for 3-point/4-point tracking, 6-point tracking, and 8-point tracking (knee), and that little bit of wrist influence will help users be able to pose more naturally with all avatars, even ones that aren't specifically fitted to them.
