Could you possibly work to make the Kotlin language adapter a built-in feature of Forge? I would gladly convert all of my mods to it if it were added. There is already an adapter mod, but I feel that it would be better to provide built-in support if possible.
Good luck with this one. The big problem with this is Forge would have to host all of the required Kotlin libraries, which would cost a lot of bandwidth (keep in mind how many people download Forge every day).
No, we will not be adding more languages especially ones that require additional libs.
Kotlin perfectly works if you use class as Mod annotation host, if you use object - these lines work(only from Kotlin 1.0.0-RC1):
@JvmStatic
@InstanceFactory
fun hack(): MainObject = this
So existing of the mod you've mentioned is redunant :P
But you'll still need to ship kotlin libs by yourself
you can shade the libs and use this bridge https://github.com/Emberwalker/Forgelin