If the latter, then there is a meaningful distinction between True Neutral and Unaligned, but it also implies a hard look at some of the ways in which alignment has traditionally been used. If you believe in the ideals of Good, but constantly fall short, you'd still qualify as Good. If you support a Lawful society, it doesn't matter if you yourself are an untrustworthy rogue. Myself, I like this approach, but it doesn't quite square with what we're used to.
This has been my preference, too, when using alignment. I've thought before that the alignment system could be more flexible if built this way, but that doing so would make it a bit too abstract for some fans that like it a little more cut and dried. Perhaps in 5E, with the emphasis on modular, they could move to the abstract approach necessary to make both readily useful within the rules:
"Alignment" is exactly what it says it is on the label--an alignment with some recognizable entity, group, power, philosophy, etc. that is strong enough to register in certain mechanics. However, what this means is defined in each alignment (or set of alignments) separately. Then you build a few separate sets for examples, and encourage these to change by campaign or preference.
You can have the 3x3 grid of Law, Chaos, Good, and Evil. Or you can have the Basic Law, Neutral, Chaos. Or the 4E model of five slots on a scale. In each of these, what it means to be aligned with one is defined in that example. That is, "Lawful Good" is going to mean something fairly close to the same thing in the 3x3 and the 4E model, but not exactly. Then you also have campaign models where it is more or less strict, i.e. when the mechanics kick in.
However, with this one level of indirection, you can also have things such as society class alignments: Nobles, Merchants, Peasants, Clergy, Outlaws. Or you can align with pantheons or factions within pantheons. You could align on geographical, racial, or political issues. In each case, the mechanics would be somewhat different.
Detect peasant alignment doesn't quite have the right ring.
With the right sets, you can even mix multiple sets. If the gods really care about deep questions of good and evil, law and chaos, but the earthly authorities do not--only about trouble, you might have one character aligned as Neutral Good Merchants -- and thus in heavy conflict with the Neutral Good Clergy character.
As far as I'm concerned, if alignments don't fuel interesting conflicts in the game, then they aren't much use. But the interesting conflicts that our group wants in a particular campaign are not necessarily the same as last campaign.