With so many Premiere users adopting the Pancake Editing setup, it would be a good idea to build this into it's own feature and develop sub features to enhance it, increasing workflow efficiency.
In a lot of cases using pancake timelines is vastly superior to pulling clips from bins.

It's easy to set up pancake timelines manually, but there are some issues that could be solved, and some other ideas:

• The Timeline panel containing your Source sequence has all the buttons and other UI elements that a normal timeline does - some of these are unnecessary for a source timeline, and just take up screen space. Examples that could be removed are source patching buttons, VO record button, Master audio track, sync locks. A solution to this could be as simple as making a new panel type called "Source Timeline Panel" or something. Another solution could be to build it into the lower half of the Source Monitor.

• The Source timeline has the danger of accidentally having a clip moved. Yes you can lock the tracks, but on a locked track you can't select a clip. A "lock in time" button would be handy. Another benefit of this is that the Source sequence will always stay consistent with an export of itself, for example when sending a low res compilation of the footage with timecode to the director, or when sending a file with interviews to a transcribing service and receiving a timecoded transcript.

• Currently you have to manually indicate which clips have been used from your Source sequence. One way to do this is to cut the section that you have used and disable it, or change its colour. It takes a few clicks, but if the clip used in the program sequence changes, the source sequence doesn't reflect that change - I would have to go back and manually leave the indication of footage that has been used. Instead, a "Frame present in Active Program Sequence" feature would be handy. It would act similar to the Duplicate Frame Marker, whereby a coloured line appears on clips in the Source Sequence have already been used in the ACTIVE Program sequence (Note the Active sequence only - in case the Source media is being used in multiple Program Sequences)

• Match frame/Reverse match frame between the Active Source and Program Sequences. Allows you to instantly navigate to the clip back in the Source. Or to find where the clip lives in the Program sequence. I presume it would be cumbersome to store extra data in the Program Sequence to reference the sequence name where the clip came from, so I expect this would only work if the correct Source sequence is already Active.

• I often start with a Source sequence containing everything off the card, and cull that down to a "Selects" sequence. That Selects sequence becomes my new source that I use to build the Program Sequence. So it will need to remain possible to create a Selects sequence and then load it as a Source.

• Currently the Source sequence is closed upon closing the project, and the workspace layout shifts to reflect that. So if you use multiple Source sequences and have to restart Premiere for whatever reason, you will need to set up your workspace again and load in all of your Source sequences and this is time consuming.

• Hide audio tracks. This would be useful when the Source sequence contains, for example, two channels of camera audio and four channels of externally recorded audio. It would be nice to only display the tracks that contain the audio required for the section you're working on. For example if the camera has scratch audio, and the sound recordist recorded 4 tracks, but you know that you only need the boom sound and want to see the waveform up large for easily finding something by looking in the waveform. It could also have a "Zoom waveform" feature that enlarges the waveform without affecting the audio gain.

• Like above, a feature for hiding video tracks. An example of this is when I use an adjustment layer containing a log>709 Lut to make the Source footage better to look at. Once I have placed the Lut on, I rarely need to touch the adjustment layer again.

• Add middle mouse button to scroll in timeline, horizontally and vertically so we can quickly navigate a sequence in a small panel, and do away with the archaic scroll bars that soak up precious space on my monitor

These are all just initial ideas so feel free to add your own.