And here I was thinking about bringing in some of the 4e changes to 5e. I'm thinking of doing away with hit dice and using healing surges (4 + con modifier for everyone) as well as giving everyone a 10 hit point kicker at the start to make level 1 and 2 more durable (Well, I guess all levels would be more durable but it would be more noticeable at levels 1 and 2). I'm also thinking about adding in the at will powers for martial attacks as manoeuvres but haven't quite figured out how to add them in with extra attacks at the moment, as in, should I scale them with extra attack or allow the effects to apply to each attack. Currently I'm leaning towards allowing the effects to apply to all attacks so that an 11th level fighter can cleave 3 times and deal their strength modifier damage to another enemy with each strike.
If I scaled them then I would probably make them kind of like cantrips that only level with each instance of extra attack and each use would use the full Attack action. A 5th level paladin cleaving would deal 2[weapon damage]+modifier to one target and 1[weapon]+modifier to a second. More overall damage but if they chose to smite, it would only affect a single target. At 11th level with improved smite, they would only be dealing that radiant damage to the primary target while the 11th level fighter would be dealing 3[weapon]+modifier to one target and 2[weapon]+modifier to a second. Feats like Great Weapon Master (or is that the fighting style?) might not be as desirable with these manoeuvres but I haven't really looked at the math to see how they compare to using the multiple attacks from Extra Attack.
But enough about what I want to do, I will be interested to see what changes you make for 4e. It definitely had a lot of options to keep up with so cutting them down would help with the learning curve for new players.