Masks should have a keyframeable transforms
Currently you have to animate the mask "Path" in order to achieve any translation. However when doing roto/tracking it would be extremely handy to be able to separately keyframe translation from the mask path. For example when applying tracking data to a mask you could track just the position and keyframe the mask path separately. Similarly when using the "mask tracker" the results are virtually unusable for any detailed roto work because you end up with a keyframe on every frame, therefore any manual edits cause popping in the animation. With the addition of position, rotation and scale it would be much easier to use tracking data in conjunction with manual roto work, and the mask tracking feature would be FAR more usable. An existing example is shape layers which have the path property separate from transform.
Jasper Rebane commented
A workaround is to create a separate layer with a mask and use it as a matte
This is also annoying to use though, I'd love to see idea implemented in AE