#1. A character change for Jeff Hardy
This could be the biggest solution to reviving Jeff Hardy's WWE career. While he is popular with fans, there hasn't been any change or character development in the last four years.
It's largely just been Jeff Hardy using his legend status and toned-down moveset in the ring. While we don't blame Jeff Hardy for having to tone down his in-ring style as he grows older, a character change is perhaps the most important thing.
The greatest wrestlers always adjust with age, and this might be the time for Jeff Hardy to focus on a more character-oriented direction over a flashy moveset in the ring. His IMPACT Wrestling run as Brother Nero was a huge success (largely due to Matt Hardy), and it proved that a character change could do wonders.
Whether it's a heel turn or simply an evolution, Jeff Hardy needs a change in personality and character. If there's going to be one last shot at the World Title gold, then that will be required.