1. Alignment is as restrictive as you make it. The problem was people seemed to enjoy making it a hard-fast system so then they could go out of their way to poke holes in it.
Thus we have paladins killing babies, and demons who can't plan, CG rogues who rape and strangely enough LE devils who are creative inventors completely unaffected by their devotion to Order.
2. I don't mind some restriction - being unaligned shouldn't let you
act like a jerk either. One of the problems I have is the devotion
people have to the metagame - that you should never do anything that negatively affects your stats. Would these characters ever stand at Helm's Deep? Or close the gateway from the Abyssal side lest Takhisis escape? Geez, what can change the nature of a man?
3. I agree that in some games, alignment lowers the fun people have. It shouldn't be a system that must be enforced. At the same time, removing it entirely detracts from the game, and I believe an optional system is beneficial. Use 'templates' that can be applied to creatures that then benefit/suffer for alignment.
I personally dislike simply roleplaying the character as a replacement for alignment, because it removes the moral dimension of reality.
I don't want to just go on racist killing sprees where the word "evil" justifies my highway robbery. I want to pull the sword meant for the pure of heart, I want to worry that tomorrow there will be no dawn because evil has come forth. Yet to have that be believable, my character has to fit into that moral-reality and has to the apparently difficult job of not acting like a royal douche.
Just as Factol Sarin refused to contribute to entropy by fighting Pentar, the character must decide the extent to which it cares about adding to evil/good/law/chaos. I can't see Planescape without this,
though YMMV.
4. Detect evil needs to be tweaked depending on the game, or just eliminated when it detracts from the fun. I like the idea of detecting intent.
:shock: 
The only one is for a paragon path from dragon which requires good or lawful good alignment (because you have to be member of a good organization to learn it).
Actually, it does, hence things like Detect Evil. It is a mechanical feature of the system. Beings can radiate evil. Evil can be warded. Values are objectified and made into a mechanical reality of the D&D world. If it weren't then alignment would be mostly pointless, as it is redundant with character conception. Any well thought out character will have a background and an ethos, which does make alignment superfluous, except that alignment is a thing that has consequences beyond the role playing element. You can lose experience mechanically in situations where you do an excellent job dramatically playing character development. There is an explicit mechanical punishment for that kind of change, which is, in essence, a mechanical discouragement to fundamental changes in character outlook.
You can do a limited range of this things, but you have to justify it in weird ways for it to really be compatible with the concept of alignment. Lawful good people cannot go about committing heinous crimes in the name of their nation state. They have to be lawful good all the time, in all contexts, otherwise it is an alignment violation. This is simply not reflective of the fact that nearly all people's moral compass is context dependent, both in terms of their culture and their given situation. They can be the equivalent of Lawful Good in one context and Chaotic Evil in another context without there being any contradiction at all. D&D says this is a contradiction, and should be discouraged, and even penalized. I would call it nuance, and see no reason to actively discourage such things as long as it is born out of role playing.
They could have. But again, I don't much see the point. What does alignment do that roleplaying does not? The only thing I see it doing is providing a fundamental moral compass for the D&D universe, one that I see as reductive and in some cases restrictive.
OK. But then why use alignment at all? What purpose does it serve at that point? Is it there just so I can cast DEtect Alignment? A "detect intent" spell can be made that fills the same role, without the objective moral judgment thrown in. I prefer a system with a clean moral slate that is not fitted with a preexisting moral framework. If I want a moral framework for my world, I will make it. If I don't want one, alignment just gets in the way.
Why should a character be penalized for an identity crisis? In the case of a God worshiping, again, alignment is redundant. The God has a code of conduct itself that you either follow or don't. Alignment is unnecessary to explain that. It is just an extra mechanical layer that need not be.
Now you've veered off into a totally bizarre tangent. I'm not advocating 4e alignment as an alternative. I explicitly stated as much in the comment you quoted from. I'm advocating not using alignment at all in any capacity. I prefer to handle morals, ethics and philosophy on a purely role playing level. If this manifests itself at all mechanically, I want that to be based on my situational judgment as a GM, not on a concrete game mechanic that follows a fixed set of rules that may or may not make sense in any given scenario.
That is I think a retro throwback to the original D&D, where you just had Law and Chaos. Why they are going that route, I don't know.