Racket splits up the iteration forms from what to iterate over (sequences[1]). You can compose different sequence constructors together, or make brand new ones, without introducing new syntax.
It has limited destructuring - sequences can return multiple values, all of which can be bound. There's an adapter to convert one that does that into returning a single list, but not the other way around. If there was it could be used with `in-slice` to be equivalent to your first example.
I could probably write a new sequence to get the `previous` behavior; don't think `initially ... then` is possible.
Lots of sequences for reading from open ports (the Racket/Scheme name for CL streams)... `(for ([i (in-port)]) ...)` for example (with an optional reader argument defaulting to `read`).