This is something I should probably do myself (fire up a playthrough of A16), and see if I agree that it was as good as so many claim.
This sounds like what the devs had talked about, during the live stream, for a future "sandbox" version of the game. When that might be their focus though, that's anybody's guess (could be a year or two, or more).
I'm about 30 days into an A16 run and it's not that great. It might be better with friends but solo is kinda boring. I can't play for nearly as long per session as I can with the current version.
But I will wait till I reach 50 days before I can give a more complete opinion.
So far, what I do like about it over the current version are certain aspects about the lighting and textures.
The desert feels like you're in a desert, with the reddish tint.
Grass in the pine forest has varying degrees of shading. In some areas the grass is more bright green and in others it's less colorful.
The burnt forest feels right. There's something I can't really put my finger on that piques my imagination. It kinda tells a story, for lack of a better phrase, just with how it looks.
The game's thick fog is perfect. You can't see anything past 15 or so meters in front of you. And since you're always in the middle of a clear patch, when you go indoors, inside isn't all foggy.
The lighting at night is perfect. Indoor dark lighting is perfect, night or day.
Zombies are weak but very unforgiving when they hit you. This is something you can't replicate in the current game with difficulty settings. Zombies feel more like what you expect from a zombie movie.
A lot of the textures are low quality, which isn't good, but they have a more realistic dingy look, which is great.
I like the assembly feature for weapons and vehicles.
As for overall mechanics and the skill systems...I am progressing much slower (which I greatly prefer), possibly because I don't know how to game the systems, and possibly because these systems can't be gamed as easily as the current ones. I go out of my way to not really learn how to "properly" play the game in its current state because I am aware how quickly you can progress.
So as of now I can say I greatly prefer the aesthetics and feel of A16, but I prefer the overall gameplay of the current version. A16 feels too aimless. At the very least, quests in the current version keeps my interest up.