Until Scratch 2.0 fully supports the PicoBoard, you'll need to use Scratch 1.4 to interact with the PicoBoard. It just so happens that the Raspberry Pi only supports Scratch 1.4 at this time, and the PicoBoard will work just fine on the Pi. Pi users are a custom-built audience for Scratch and hardware such as the PicoBoard.
If you run a Linux-based system, then your choice of Scratch versions gets more complicated. Adobe, the developer of Flash, has announced that it's no longer supporting AIR or Flash on Linux after Version 11.2 of its player unless you're running the Chrome browser. Adobe and Google have a deal to provide a Chrome-only plugin. If you work in an open source operating system world, then you know the intricacies and frustrations of managing mainstream software from companies such as Adobe.
We won't get sidetracked here. Just know that if you're on an open source operating system and you have problems with Scratch 2.0, then seek out the 1.4 Version. You'll still have a great experience.
Note
The bottom line is that it appears as if Scratch 1.4 will coexist with Scratch 2.0 for the foreseeable future. Your chances of encountering 1.4 are great.
Scratch 1.4 is available from the following resources:
Installable version: http://scratch.mit.edu/scratch_1.4/
Source code: http://info.scratch.mit.edu/Source_Code