Thats a good question, I did meet one guy on Palace who was going to make a new version of instant. But that was 2 years ago lol.
I did see a version of The Palace Viewer working, well connecting but completely one giant bugfest really. So for now my advice is: don't hold your breath. None of the developers seems very intrested in a new Java client.
the new Palace 3.6 client is pretty cute thought, you can check it out here:
Its only the program, just put it in your Palace folder and run it.
Its only a newbiew friendly temp solution until the real replacements are finished. More on that later :P