You can embed NativeScript into any existing iOS app for ad hoc usage.
NativeScript has matured greatly over the past couple years and part of it's maturity is increased extensibility.
Read more here: https://blog.nativescript.org/embed-nativescript-sdk-ios
git clone https://github.com/NativeScript/embed-sdk-ios-sample.git
cd embed-sdk-ios-sample
pod install
Now open the MyCoolApp.xcworkspace
to run it.