Here is the how I would like 5e/Next battlefield to look. This is in general terms without getting too much into actual mechanics. I am going to focus mostly on the 4 main classes and their combat roles/abilities.
Fighter: I want the fighter to primarily be the badass on the battlefield like he was in 1e (yes I know some disagree with this assessment of the 1e fighter but it is my opinion and I am sticking to it and won’t debate it in this thread). He should have the most HP, the best AC, and consistently hit the hardest in straight up (i.e. non-sneaky) situations.
Secondarily I would like him to be the defender. He won’t defend through his own abilities but the general rules would allow him to defend by being the badass (he may have some abilities that help this). I would like to see shifting go away (or at least be limited to moving around a combatant instead of away from him) so that once the fighter is adjacent to a foe that foe would suffer an AoO if he tried to get away from the fighter. Maybe the fighter can have access to a pulling mechanic that gets foes adjacent to him. No marking, no (or very little) defender mechanics.
Rogue: The rogue would have crazy good movement abilities. He could move around or past foes without generating AoO and could attack at any point during his movement.
So an example that combines these two classes would be: a fighter is engaged with three orcs. The rogue starts 3 squares a away from the closest orc. He moves three, squares attacks the orc (he would get his sneak attack), and then moves three more squares and is out of the orc’s reach when the orc starts his turn. The orc cannot pursue or else the fighter can give him a good whack as he moves away.
Wizard: The wizard would be a combination of old and new. He would have an at-will attack or two that wasn’t very strong (but not exceptionally weak either) and then he would have his Vancian spells to provide better attack options from time to time.
Cleric: I would like to see the cleric go back to being the knight-type that 1e described him as. He would have heavy armor and could stand in the front line with the fighter-types (possibly doing some defending) and use his magic to buff his allies and de-buff his enemies. He would have some offensive capabilities sometimes (an occasional flamestrike). He would do most of his healing outside of combat. I wouldn’t want to go back to the blunt weapon thing of 1e though.