Our X platform is still largely Java-based, and our tech stack is: 

• Java Server Faces (JSF) for the UI components
• Java and IIS for various middleware components
• MS SQL Server and Amazon DocumentDB for data storage
• Apache Kafka and Storm for inter-component messaging

We host with AWS. 

JSF focus is to - as quickly as possible - re-work the existing UI, to give it a more contemporary look-and-feel. At a later date, we may choose to change the framework (e.g. to Vue.js) but that's a longer-term decision. In the interm, we may consider using something like Primefaces to extend the UI appeal. Upgrading the version of JSF that we use (from JSF2.1, with Richfaces as the 'skin') would likely be the starting point, with consideration towards using Primefaces. 

I would say that "confidence will be key"... to take an existing JSF2.1 application and make the UI sing (e.g. by using a better library of componets, such as Primefaces). Experience on that specific journey would be ideal. If someone isn't entirely confident about JSF - e.g. because it's been a while since they last used it, or they didn't use it extensively - then I'm not sure that we'll achieve the speed of outcome that I'm hoping for. 

UI/UX will be a separe role. 
In case of changing the framework to something else we will extend the team with FE dev.