The point is, the more they can spread the matches out away from each other, the more the broadcasters can charge for adverts.
Moving a match to Friday, means less competition at the 3pm kickoffs.
Now you have 8pm Friday, 12:45pm, 3pm and 5:30pm Saturdays, 1:30pm, 4PM Sundays, and some 8pm Mondays.
So that becomes 7 featured matches instead of 6 for some weekends.
So expect the big teams to be moved there or rotated there.
I'd expect opening weekend that season for 2 good teams to feature on the first ever Friday night broadcast. Don't think they'd have a derby there but something like Arsenal v Liverpool is what i'm talking about.