We are planning to add NativeScript 2.4.0 (Experimental) support in AppBuilder with our next major release, which is planned for the end of November. Experimental framework versions have not been thoroughly verified and you might experience issues when working against them.
Additionally, we do not have the practice to update project automatically. However, after AppBuilder 3.6 is released you could migrate your NativeScript project manually
I hope this helps.
Telerik by Progress