This change actually removes features that the GPLv3 had. In particular, the main one and the reason most companies would want to buy a commercial license now is the Grid component. I understand their complete package will have ASP.NET MVC bindings but those aren't necessary.
So, in a way, this is really bad news for open source projects as it effectively takes away a component that is at the heart of why Kendo UI may be used instead of jQuery UI.
They have in effect basically screwed over completely open source projects. For them the only change is that they lose functionality.
But, Telerik is a for-proit company and they've always struggled with the licensing for this as they didn't know how it would fit with their commercial goals. I don't think they've got it right now.
Personally, I see no reason to use this even now. jQuery UI is not maintained by a commercial company and is just as good. I can be confident that the license for jQuery UI isn't going to be messed around with based on new corporate goals. The Kendo UI versus jQuery UI site does a good job of doing the comparison but without the grid component, its a hard sell.
EDIT: I do want to add that overall this is great news. I'm pointing out the nuances of this decision. For people already using this and don't need the other components or can find substitutes, it makes sense to continue to use it and not have to buy licenses. Also, I hope Telerik somehow addresses this and not ignore it.