In addition to this, the release duration is somewhat experimental.

Why such short support windows? The strawmen of three months between releases and a one month grace period are ridiculously short support windows. The reason I propose them is because- like I mentioned in the design goals- we want the smallest delta from how people work today. Right now, there is no concept of stable versions, and we're trying to introduce it. Starting off with a more standard support window of something like two years would be a radical shift in how library users and authors operate today. Three months is very short, but it's long enough for us to test the process. As time goes on, we should have serious community discussions on how long a support window we should have. (I, for one, am fully in favor of extending it well beyond three months.)

so "1.1" is the version of the whole thing, even if most of the packages haven't changed; as opposed to the usual way of versioning each package independently?

edit yep, looks like it: "an LTS Haskell release reduces it all to a single version number for "my Haskell ecosystem""