The first Quest 5.0 Technical Preview version is now available.
This is a very early release. Most importantly, it's limited to hand-coding games (there's no visual editor yet), and there's no support for games for earlier versions of Quest. These features will be added over the coming months/years (it's going to be quite a while even before the first proper beta versions).
You can download it from the new Quest 5.0 wiki at quest5.net
If you have any feedback or questions, please drop me an email or see the forums.