i am pretty sure ffg will do the 3rd and 4th act in the next Expansion. simply because this is the only way they can go furtther with 2ed.
remember path of legend, nobody thought about something like this to come in 1st ed.
so i think the next Expansion will be a pretty big box with not only normal 1 and 2 act campaign but also additional rules and material for 3 and 4 act.
you may say this will make it necessary to create new Monster Cards and additional class deck cards for each class. Monster Cards were all new in road to legend too. instead of new class cards for all clases they make just additional cards for each archetype, every class of that type can use. put some more dice in it and thats it.
i am pretty sure it will come.