I have seen talks and/or papers on all of these except Scopes and Gleam. Out of the list the only one that does not provide something I am interested in is Unison. Given that your feelings for interesting language features seems to be at least marginally close to mine I am going to check out Scopes and Gleam just to see what they have that interested you.

Personally, from a conceptual level, I find that Koka and Roc provide some of the more interesting developments in PL design. For anyone wondering, as to Roc (which I don’t think has an implementation or even a full description yet) I am particularly interested in their concept and implementation of the ‘platform’/‘application’ layer idea. As to Koka, the papers the team has generated are almost all excellent. The paper describing Perseus, the GC/resource tracking system, and the compiler implementation review are stunning.