Depends on your definition of syntactic sugar - for instance, the coroutines stuff is very intuitive and makes code far more readable and easier to work with. It all compiles down to stuff that a Java decompiler will be able to read back to Java.

But that's just one example and a subjective one at that. Not everyone will feel the same way and for those who don't there's no compelling reason to 'start using Kotlin' - if what you have works then stick with it.

There's also Kotlin native and Kotlin JS - allowing Kotlin code to be compiled to native binaries as well as to javascript is pretty compelling and will (imo) pay dividends. Both are still very much in development though.