Can't make an update that fundamentally changes the core game as a paid update, no matter how the LEP people would wish to think otherwise...
Next years update however will be adding completely new 'things' to the game, and thus rightly justifies a price tag - and LEP buyers can whoop with glee.
Source? 4.0 is already going to be free, which would make charging for 4.x a bit odd. At present rate 4.x is going to take us well into 2020.