No plans at present to add additional language support. The reason is that for each new language we add, there's an ever-decreasing amount of growth in the use of the product, but the maintenance burden gets larger because of the increased surface area we need to test.
I'm not super knowledgeable on the JVM. Can you consume the (Pulumi or otherwise) Java libraries in any JVM language, or are there additional bindings that have to be written or maybe some particular interface a JAR would need to conform to?