I think it would be generally pretty helpful for adding animation on the timeline if we could have the masking tool that is in the Motion Puppet available to use in the Modify panel directly. This way it could be used for any motion inserted from the Content manager, and hopefully, be able to overlay (blend) with existing motions on the timeline.

For instance. I would like to first add a walk motion to my character, and then mask out the pelvis and legs, and add a conversation motion. The end result would be the character walking with the upper body performing a conversation motion at the same time.