If you just simply want to have multiple animations overlapping and blending among them, that’s a “default behavior” of Sequencer. All you need to do is to adjust each weight of animation track. And, my post was to describe how to blend animations as filtering specific body parts in Sequencer.
One thing that I’m not clear with your question is: you said, “Say you had a “Body_Idle_01” animation and a “Body_Idle_02” animation overlapping on the same body track. .” You mean on the same body track as one animation track? “Body_Idle_01” animation and a “Body_Idle_02” can be blended as two animation tracks together, but not as one track. I hope that I answered your question.