There's a lot of untapped potential for new stories within the narrative time skips of the Dragon Ball series. Dragon Ball Super is a prime example of this; the entire series thus far has been set within the 10 years between the defeat of Majin Buu and the 28th World Martial Arts Tournament. Perhaps a similar treatment could be given to the other time skips throughout Dragon Ball.
A good place to add more material for the series would be somewhere between the end of the Cell Saga and the beginning of the Buu Saga. At seven years, it's the second-longest time skip of Dragon Ball Z after the aforementioned 10-year time skip. If there was a good opportunity to tell interesting, action-packed stories that weren't present in the original manga, it would be here.
One thing that could be focused on is Gohan's time as Earth's greatest champion, as Goku meant for him to be. He never really got a chance to play the hero in the Buu Saga, so this would be a good chance to let him stand in the spotlight. This kind of happens in the Bojack Unbound movie, but it's non-canon and doesn't give Gohan this moment until the climax. A longer series would give Gohan a better chance to be the protagonist fans always wanted him to be.
Another good thing that could be covered between Cell and Buu is Goku's time in Otherworld. As the DBZ narrator put it, Goku had an infinite amount of time to explore the afterlife. This must mean that there were plenty of things for Goku to see and do while he was dead.
Covering this time period would also be a good way to reintroduce aspects of the Other World Saga into the official Dragon Ball continuity. This anime-only arc has a lot of things that feel like they would be integral to the lore of Dragon Ball, including the other Kais and deceased residents of Otherworld. The Otherworld Tournament, in particular, boasted a wide variety of cool new opponents for Goku to face. There are definitely those out there who would like to see Pikkon make it into the canon.
Besides Gohan and the Otherworld, there are plenty of other things that can be covered. There's also the birth and upbringing of Goten, Vegeta rediscovering his will to fight, Krillin starting a family with Android 18, Dende easing into his new role as the Guardian of Earth, and more. A lot can happen in seven years, so there should be more than enough time to cover all of these side stories.
Unfortunately, there are no official plans to cover the events between Cell and Buu in depth. The DBZ anime has some non-canon snippets here and there, but nothing concrete. Akira Toriyama will answer questions about this time period in interviews, but he hasn't expressed any plans to write a full-length story. The larger stories that may or may not have happened during this seven-year gap remain undisclosed.
It's possible that the upcoming Dragon Ball Super: Super Hero movie will mention this time period. The antagonists of this movie are the Red Ribbon Army, who might have begun their latest plans as far back as the Android Saga. It would make sense that they would want to pick things up where Dr. Gero and his androids left off, especially after the defeat of Cell.
As fun as it would be to cover the events between Cell and Buu in detail, there are no clear signs that it will be happening any time soon. The best one can hope for are bits and pieces of this gap in the timeline to be filled in at infrequent intervals. Until then, this time period will remain largely a mystery.