I don't know much about 4e, but what's the difference between unaligned and neutral? Choosing an alignment that's not an alignment just sounds munchkin to me.
I know a guy who runs his 3.5 game with no alignments. It works for him most of the time but it takes constant reworking of the rules, and game balance is often skewed because alignment is also a game balance tool. With complex systems like 3.5 it's often a slippery slope changing things and alignment isn't as insignificant as it may seem at first.
Without getting too far off topic into a discussion of what alignments mean, I'll say it would be nice to have more definition in the rules as to just how to apply it to common situations. The ubiquitous scenario "Do you kill the baby orcs?" comes to mind.
But I digress... changing stuff, especially iconic stuff like alignment, so drastically in 4e does seem to be driving all the "does it still feel like D&D?" questions coming from 5e development. My playgroup didn't think about changing editions until years after Pathfinder had come out, but it was that exact thing that made PF much more appealing than 4e. And I think brand identity in the internet age is worth a lot less than the bean counters think. Branding didn't stop eveyone I know from choosing Pathfinder instead of a less attractive "D&D" branded option. That said, not many of us were happy about that either, so maybe brand identity does count for something... just not what they think.
Unaligned means just that: you are not aligned. Not some sort of Swiss bank, mediation type of stuff. You just don't play that game. You may have your own personal ethics, but you just don't align with the cosmic forces; you're an average joe just trying to live your life. IMO, it is what neutral should have been. You're not concerned with some sort of cosmic balance between good/evil or law/chaos.
How is alignment a game balance tool? I mean, sure, in 1e paladins were saddled with a lot of alignment restrictions in order to balance out being a fighter++. But I think we can agree that that particular form of balance is a design best left in the past.
Furthermore, I would say D&D needs
less emphasis on alignment, not more. That is what 4e did, it was not nearly as tied into the system as in previous editions. Sure, demons, paladins, undead, angels could be affected or detected by certain spells/powers, but it is very limited beyond this. To me, I have always played D&D
in spite of its hokey alignment system, not because of it. So I find it less of 'feel like D&D' than many others. Sure, In epic fantasy you have various good vs evil themes, not to mention beings that tend to embody them, but that does not call for forcing everyone into a 9 tier alignment system. To me, Pathfinder, despite some good adventure material, was a warmed over 3.75, a system that I grew tired of before Pathfinder even came out.