my answer will be short - NativeScript will be open sourced under the Apache License, Version 2.0
. There are no other limitations!
There will be paid tools and integration with other tools and platforms coming from Telerik (and other companies), but the framework itself can be used and extended in a way you want, complying with the Apache License, Version 2.0.
Please drop me a line on email@example.com and we can talk about possible integration/partnership.