Building on Premiere's current ability to open sequences loaded into the source monitor, it would also be very handy to be able to view single clips in a timeline that are loaded into the source monitor. The timeline itself wouldn't be editable, so perhaps it would have a much more distinctive look from the main timeline.
We could also extend this feature by grabbing a selection of clips from our mainline and placing them into this phantom timeline from which we can insert and overwrite from.
And yes, this has been inspired by a certain other NLE.