"Blossom will use the GPLv3 license, with commercial licensing similar to the Sencha model."
I don't have a clear idea about what's going on in the SproutCore community, but I don't think this has universal support.
One of the reasons we rebranded to Amber is that our codebase is inspired by SproutCore 1, but it is a complete rewrite, targeting a smaller file size and web-centric development.
All of the fragments of SproutCore 1.x target native-style applications with a ton of JavaScript, while Amber targets ambitious web-style applications using HTML and CSS for the presentation layer. Amber apps don't have much in common with SproutCore 1 (or "blossom") apps, so a clean naming break felt like a clarifying thing to do.
i.e.: sproutcore.js/blossom - "desktoppy" MVC framework with HTML5/js as a display layer
amber.js - "web-appy" MVC framework with HTML5/js as a display layer?
*edit: