I think in practice most people have a single dev environment and production environment and effectively only have like one person actively doing things at a given time, so I will agree that in practice, the environment/publishing process is a little bit overkill for a lot of people. But I do have clients with a lot of non-prod enviroments and various dev/qa teams working independently and I can see this helping out (somewhat..) with the "too many cooks in the kitchen" scenario, and I think ultimately that's what Adobe was going for. I'm kind of hoping in the future Adobe might make an "E-Z Mode" version of it for the average Joe who doesn't actually need this layer of flexibility, but.. I'm happier that it's there if needed, than not at all.
But as far as updating environments. Yes, you can do that, though to be fair, I think maybe Adobe can make this a little bit easier to find. Namely, add navigation to it somewhere on the Environments tab. Currently you can just add delete an environment on this tab, and clicking on an existing environment only lets you update top level stuff like the name or adapter, not assets within it. I think Adobe definitely needs to add functionality for editing the assets themselves here. Or at least a link to where you edit it (see below).
But as for actually editing assets within an environment. Go to the Publishing tab. Then under the Development column, you should see the list of libraries (environments) you already have. You can click on their name or the down arrow on the top right of the an individual box, and you should see an Edit option.
Now.. gotta be 100%, this page could use some love. It isn't immediately and easily made clear / intuitive what is currently in the library vs. what is not. But there is an Add a Resource button where you can select from a menu of Rules, Data Elements, and Extensions, individual assets. And there is an Add All Changed Resources button that is generally all you really care about most of the time.
Note that you can click on the library (environment) when it is in the other columns (Submitted, Approved, Published) and view what is in it, but you cannot edit it. If you want to edit it, you have to reject/demote it back to the Development column.
