Integrating Kotlin via a feature-first approach is not without its drawbacks. For example, if new features are being developed with a new language, there may be a temporary decrease in developer productivity as they learn the language and get comfortable with new idioms and features. Anecdotally, this dip in productivity is generally considered to be minimal, but it will absolutely depend on the individual developer experience and team dynamics.
While shipping a new development language to your production users can be exciting, it also comes with some risks. You may need to closely monitor your first Kotlin releases to verify that features such as lateinit or non-null properties are being used correctly across the entirety of your user space.