where's the right place to request features?

https://kotlinlang.org/community/ has many links. I believe the issue tracker is the place to start. https://youtrack.jetbrains.com/oauth?state=%2Fissues%2FKT Depending on the feature, you’ll need to follow the KEEP process. https://github.com/Kotlin/KEEP

Depends on what kind of features. New Language feature/Syntax? Something to be added to the stdlib?

extensions of existing features syntax to other areas

I personally would start with presenting the ideas + problems that they solve in #language-proposals to get some feedback from other developers/JB guys. Thereafter you can start writing a KEEP that describes what the feature/syntax is for, what problems it solves that can't be solved/are hard to implement with existing features, how it interacts with other language features, what its limitations are and so on