He’s main evented and won those matches at NXT Takeover: Brooklyn and London as well as being a winner of the Dusty Rhodes Classic. He’s done it all, and his jump to the main roster is not a question of “if”, but when.
However, there is some concern within WWE about Balor’s long term health. Those within WWE are concerned about his body breaking down as the poster boy of NXT as the brand tours even more in 2016.
Finn Balor is being built as a big moneymaker for WWE and his time in NXT is being designed to get him ready for the main roster. The concern is WWE brass doesn’t want to break him down in NXT when he’s being primed to be a superstar for the main roster in the future.
That only fuels the speculation that Balor will be on the main roster sooner rather than later. If WWE wants to make him a superstar, he’s on a great run to do so right now.