Not sure it's quite 90% android but it was always going to be the case given that Android has to date been the environment where Kotlin has gained the most traction. I too am more focused on server-side development and it is possibly a more difficult environment to break into given the existing players & less obvious immediate benefit of using Kotlin. Kotlin's time on the server will come and there are several speakers at Kotlin Conf who I'm v keen to hear.