I think you have to weigh the importance of the internal application and it's need for a rewrite. It just may not be worth it. If you do, I would recommend web,

I think you have to weigh the importance of the internal application and it's need for a rewrite. It just may not be worth it. If you do, I would recommend web, but you'd still have a significant JVM-based-language backend I'd assume since you have to use RMI as your communication protocol. I personally would not do JavaFX because you aren't really stepping up enough to make the rewrite worth it.