Another option could be to internally implement a top sorting criteria
as ratio of
The number of channel episodes already placed in the playlist
Total number of queed channel episodes.( Placed+to be placed)
So channels 25/50 and 2/4 will be treated equally, and other sorting criteria will be evaluated.
OTOH, for numbers below, the big channel would be preferred for the first case and small one for the second case.
25/50 and 3/4
25/50 and 1/4
P.P.S.:Perhaps better to evaluate the queue scores not at the end, but at the beginning of current episode playing. In such a case the queue would be pseudo-static during the play, allowing the manual user intervention - like e.g. move as the next played episode or move to the top etc.
P.S.: As the queue ranking would be dynamic, there would be evaluated at the end of the current episode playing, what episode should be the next one.