Presently, Premiere Pro has sync locks. If you want to perform an action like insert or extract from one or several tracks, but you do not want this same action to occur to one or several other tracks, you can click on the sync lock icon of the tracks you do not wish to be affected.

However this proposition often works in reverse and Premiere does not cater for this in an elegant way. For example perhaps you are editing a project based around interview and B-roll. You might keep B-roll on video track 2, interviews on track 1 and also have multiple audio tracks underneath. If you want to make a change to the B-roll only and do not want to affect any interview video tracks, or any other audio tracks, you currently need to switch off sync locks for ALL THE OTHER tracks rather than for the ONE track that you want to affect.

A better system would be one where sync locks affect synchronisation of editing actions such as insert or extract, both exclusively and inclusively, rather than just exclusively as they do now. Under my proposed system, clicking to disable the sync lock on video track 2 means that anything I do track 1 or any of the audio tracks, will have no effect upon video track 2 (just as already happens) but ALSO anything done on track 2, would not affect any other tracks because synchronisation is switched off. This would also be the case for multiple tracks where synchronisation is switched off, it means 'exclude these tracks from syncing with actions performed elsewhere, and include these tracks in the list of tracks that do not affect others'.

At present, if I turn off sync lock on track 2 and perform an extract edit on that track, all other tracks on the timeline whose sync locks are switched on, will also undergo an extract edit. While I can still achieve what I want to achieve with the sync locks, I would have turn off all sync locks for both video and audio first, which is a waste of time, especially since that time has already been spent deliberately choosing that video track 2 not be synced with other tracks.

This is a more intuitive understanding of what a feature called 'sync' lock would do as 'sync' presumably stands for 'synchronise' and typically most people would assume that actions performed on a track whose sync lock is switched off, would not be synchronised with other tracks on the timeline just as they can currently correctly assume that actions performed on other tracks won't be synchronised with that one either.

UPDATE: I've added a gif of what I'd like to happen. You can see here I DISABLE sync locks on two tracks (4 + 5) where there's titles and then extract an in and out range on those tracks. With bi-directional sync, Premiere knows that this extract edit is to be performed ONLY on those tracks and does not extract anything from any other video or audio tracks. Conversely, because sync is ENABLED for all the other tracks, I can also perform a ripple edit on track 1 and the ripple will be synchronised with all other tracks EXCEPT 4 + 5. This is sync locks working bi-directionally.