I don't have a release date yet. I'm not sure what all is going to be updated.
Upgrades to Horizons through the 1.X versions will be free. It's far to early to think about a version 2 yet.
As far as previews, I don't have any plans as of yet to make a preview, but I will install new modules to the sample game engine as they're completed. One that I know will be added to Horizons is a Staff List. There is already an explore page that was added to the sample site.
http://samples.phphorizons.com/index.php?p=exploreIt's a page that takes all the links from the drop downs and lays them out on a page in a "site map" form.
If you have suggestions, I do entertain suggestions Features Request forum ->
http://www.phphorizons.com/forum/viewforum.php?f=14&start=0