I frequently have to mix together several sources, and the Multi-Camera Source Sequence in Premiere Pro should in theory be the best way to go.
However, it's seriously underdeveloped and for a single camera with separate audio, I end up doing a sequence instead.
Mix and scrub audio in Audition, tag and comment source video in Prelude, import both to Premiere Pro and put them together on a sequence so I can use that sewuence as a source for other sequences.
Why don't I use a multi-camera sequence? Because you have to tag syncronization points before you put everything together, because audio and video is often recorded out of sync, with several video recordings per audio recording etcetera. It ends up a mess. We don't live in an ideal world, and not wanting to waste time (and make the talent lose focus) organizing things, recording happens pretty much on the fly with all that includes in differing methods, ideals and so on. We need to know how to cut resources (and this includes not using the most exåensive editing tools) but there's always room for improvements.
I like to slap everything loosely together post-production and fine-sync on audio waves on the run, but this means you can adjust the multi-camera source sequence after you have put it together.
This isn't possible in Premiere Pro, at least not without putting it into a sequrnce first and that's the next step you want to do after all the syncronizing is done, not something you want to while cutting up the sources in a sequence.
I believe most of what I need for this is already programmed but it's mostly a matter of politics. Just please understand, synchronizing and preparing sources is different from working with a sequence, but it can be a substantial piece of work on it's own and it's not enough to just put it together in a menu and think that's all fine. (And not by far at that.)
What I need is to be able to edit a multi-camera source sewuence on a timeline like I would edit any other sequence. And call it a multi-source sequence, it isn't just video.
Then audio from different sources can be mixed together on the timeline like you do in a sequence, expoerted to audition as a multi-track session for more advanced audio processing (and no, single tracks aren't enough, I often need the real-time effects in audition not just the processing of whole tracks. And I mix together several audio sources, both mono and stereo tracks some from cameras but mostly from a separate, 24-bit audio recorder with inputs from hand or tie mics, environment and perhaps a gun with a boom. (I'm the audio guy with perhaps a camera on the side, others handle the main camera(s).
And video from several cameras can be put together, one track per camera on a timeline and not just one clip per track, one camera can have several clips taken on a timeline.
Then, when all this is put together it can be used as a source, like we use a multi-camera sequence today.
I believe it's possible, and would increase the value of your offers. If this isn't done, I may end up looking for other software.