Follow-up from "skip tracking elements without trackable sources"

The following discussion from !1689 (merged) should be addressed:

• @BenjaminSchubert started a discussion: (+3 comments)

  Will this still mark the element as skipped in the pipeline? Or do we decide to not add it at all in the pipeline?

defer filtering non-trackable elements until TrackQueue.status() to communicate element track is skipped for case of untrackable sources. This will be a bit simpler after _update_state is removed

see 9cb56c81