Regradless of how much effort it would take to create a Kotlin-to-Java converter, creating such a project will run counter to the goals of JetBrains with regard to spreading the adoption of Kotlin, and therefore we have no plan to build it (or to improve the existing Java bytecode decompiler in IntelliJ IDEA so that it would handle Kotlin-generated bytecode better).
Using Kotlin as a source-to-source preprocessor would deprive you of most of Kotlin’s advantages (null safety, making it possible to build concise and idiomatic APIs, and so on), would result in a much worse workflow in terms of debugging (how would you fix issues if the debugger shows you the Java code generated from Kotlin? how would your colleagues do that?), and will not result in any objective advantages other than satisfying organizations that are “unwilling to change” without providing any motivations behind said unwilling.