I am doing something almost similar, it's not a boilerplate by definition, but people could use it to start their projects, it's still under development and I may take some time to finish it, but...
I am using clean architecture (with some modifications), in my case, view, database and network are platform specific, presenter, usecases and repositories are Kotlin/Native, it's far from perfection, but maybe it could raise some good ideas
https://github.com/alandoni/MultiPlatform-CleanArchitecture