I think they will never relese the 64bits because probably they lost the source code of libncui to recompile it to 64bits.
I have already ask to our sales guy and it not even in the guide.
Hey, don't take my word as granted... I'm just a SA admin... not afiliated with Juniper... wait for Juniper answer.
There has been some discussion for the past several months and this is on our roadmap, but I cannot give a definite timeline. My suggestion would be to file an ER with your account team so they can properly provide you updates on the latest developments for a 64-bit version of Junos Pulse for Linux.