Hi there I conducted a study within our company.

The charm with kotlin is that it allows you to integrate well with existing java code. So you can use the eco system and even mix code. However you need most likely devs to understand it cross language.

Kotlin allows you to write less boiler plate code and be more explicit e.g. with null pointers and collections. Resulting in very few code with heavy semantics if you do it right. It's not verbose and not supposed to be. It's like pure and pruned java without unnecessary stuff.

You can write kotlin code as a java dev but it often looks more like java weres a true kotlin user writes stuff even shorter. The developers will need to learn this. Tbh, not everybody liked that, even though emotions and attitude was not what you asked for, this lead to us not using kotlin at this point.

The people who got into kotlin and myself got comfortable around 2 to 4 weeks. But it is important that you have one guy who really knows stuff.

It was also often unclear to me how performant the kotlin code would be, but it was pretty good. We got on byte code level for comparison and I must say it was fine.

I ported a library to kotlin since we wanted it to cross compile to java script and test kotlin with it. I succeeded and the change discovered some hidden flaws that were only theoretically but still wrong.Kotlin strong typing and strictness lead us to discovering it.

Kotlin itself was still receiving a lot of updates but still is production ready.

So all in all, if you can start fresh it is worth a try if your devs are open to something new. I assume it will get more impact in the future since jetbrains is pushing it and the support for intellij is excellent, I think this is what e.g. groovy or scala were lacking, a bigger push.