I posted this somewhere else, but I'll share again.
My #1 desire for it is to be able to pop out individual streams into their own windows while they are sharing the same video player settings, so if I pause one, they all pause, and they are all synced together. I have two monitors, but with proview as it is, I have to keep it on a single one. I'd love it if I could have the proview on my main monitor with the main stream on the second with the sound of the casters.
I tried to do this by having two instances with the eye button to share, but when I click in and copy the link into a new tab, it just shows the vods page for proview. Maybe this is because it doesn't work with vods, maybe it's an issue on my end, or maybe the functionality isn't there to have two synced connections on one computer. IDK.
I'm not a dev, so I don't know the complexities of popping out individual streams but staying synced. Might be hard when considering VODs (which is 90% of what I watch).
An alternative, or additive, feature could be allowing listening to the cast on any stream. So I can watch a single instance of proview, but listen to the cast as well. It would be could if there was a button that swapped between the main stream and the last proview you had up. So I could watch a top laner, maybe he's off splitpushing, and I hear in the cast that a teamfight is happening. I can click the button and watch the main stream and then after the fight swap back with the same button all without losing the cast audio. I know this is possible right now with the select stream button in the middle, but doing that interrupts the action.
Like I said, I'm interested in proview and I don't regret my purchase. I think it's a good first step and, with some adjustments, I might pick it up again in the future.