I noticed in another standalone player just released that they support multi channel by playing in multiple windows (side by side, or top and bottom) rather than picture in picture, I think that's actually a better solution as nothing is obscured from overlaying video
That's very interesting @jokiin . Do you remember which player it was?
I thought most users would be interested in PIP only. Side-by-side or stacked play is probably easier technically than PIP.