I think only the American system really justifies a playoff system. However you then have to break up the league into divisional system.
Which would bring on the moans of, there are not enough players there are too many easy beat teams.
However the divisional system allows for almost unlimited expansion of the game without having to sacrifice the traditional clubs. It also justifies the licence system properly. If you tick the boxes your in, if not your out. No need to fiddle the criteria to fit some arbatary league limit of clubs.
Also clubs need not complain about not having enough derbies and no complaining about too many games in a season.
However I think this boat was missed at the Start of SL and as turkeys don't vote for Christmas and SL clubs control how the Christmas pudding is split. I can't see it happening unless SKy pull the plug on the funding or strangely offer a huge increase in funding.