Happstack 8 is still happening.
For a while now, a lot of the work has been focused on things way out in the wings. That includes a major effort to unify and improve the stripe haskell bindings:
And a complete rewrite of the happstack-authenticate library which is better suited for modern single page application web development and JSON clients.
And, of course, work on clckwrks and apps built on clckwrks.
However, returning to the core libraries is back in sight. The aim is to start at the bottom of the stack and apply the things we have learned from building large applications on top of the existing system.
The first piece will be the new low-level HTTP server -- hyperdrive.
Most of the tech needed to build that has been worked out except for the user configurable 'scheduler'. I need a couple free days to finish thinking about that.
Unfortunately, there is currently no ETA. Not because Happstack is not a priority, but because I am too busy using Happstack.