It’s being reported by F4WOnline.com that WWE does have longterm plans for NXT Champion Finn Balor to make his debut on WWE’s main roster. However the short term plan going forward is for him to continue to be the face of the NXT brand which means Finn might not get called up until the end of the year.
Samoa Joe possibly beating Finn Balor for the title at NXT TakeOver: Dallas is something that’s being discussed. But Joe winning the title is not a lock.
It’s also been rumored that WWE might have Joe make his main roster debut the day after WrestleMania 32. Whether or not that happens likele depends on the outcome of his match with Balor at TakeOver.