Hi there Kenichi, and welcome to the forum! I hope you stick around and have some fun here.

Now, as far as your question goes...I honestly don't know if we'll ever get something tackling that time period or not. It's almost like there's a stigma around anything with Pan or Uub, like people look at them more as GT characters, even if they first appeared in DBZ. Our most recent new animations for the franchise have typically avoided that area - the 'Goku and Friends' special was from after Buu's defeat but way before Uub comes into play; 'Episode of Bardock' would seemingly take place years and years before the series even begins; 'Plan to Destroy the Super Saiyans' would seemingly be in the Androids/Cell arc somewhere. Even the upcoming new movie, 'Battle of Gods', takes place 'several years after Buu's defeat', but still has to take place before Uub and Pan come into play.

I for one would love it if we got a story taking place actually after the end of Z, showing more of Uub's training, even if it did something to completely disregard GT - but it's tough to say if Toei will ever actually be brave enough to venture into that time in the story.