I too really like those three rules.
Second Wind gives a very cinematic, of muttering through the pain and forcing yourself back into the fight. Also while it may not entirely get rid of the need for Healers; Second Wind, Potions and Heal-Checks can make it less necessary.
Action Points also very cinematic, it is when you have stretched yourself to your limit and give into that one last reserve of strength to pull off one more thing. I would like though as a optional rule, some kind of negative effect to show this, perhaps certain skills/roles have a bonus if you have a Action Point available, or it takes -5 (scaleable) off your Healing Surge when there is not a Action Point, something.
Bloodied, once more very cinematic and gives a bit more flare and variety to combat. It is no longer simply repeating the same actions till either side is dead. Now with Bloodied, half way through the fight the action surges again as PC/enemies grow weaker and the opposing side takes advantage or this weakness causes special powers to awaken, ie: rage.
With Milestones as people have stated it can encourage people to go from encounter to encounter. But also, I am hoping the Milestone: 2 Encounter is simply a base formula for simple things.
I could very well see either through official rules or houserules where certain abilities or items only becoming usable after a Milestone is crossed and these Milestones are true life-changing or atleast campaign changing Milestones. Heck Quest Items could have built in Milestones for a Quest.
So:
Item: Key of the Door (Implement)
Ability: May open a Gateway to the Feywild
Milestone: Must first find and be blessed by a Eladrin Priest to activate.
There could be tons of interesting Milestones this way.
Or perhaps certain items/charater abilities/plot points can only be activated or begin to become awakened after a series of different Milestones. This could be called a Pilgrimage (taken from Promethean) where a Pilgrimage is a series of Milestones one must cross to complete the requirement for whatever the items/charater abilities/plot points are.