I'm highly skeptical of such being truth because:
- If a renowned mangaka was trying to buy Dragonball from Toriyama, everyone and their mothers would know about it. Yoshiyuki Tomino sold Gundam back in the day and none of it was in the shadows.
- Japanese authors, be them of manga or games, usually don't give a flying fuck about US/Europe. Various artists, including Kishimoto, have said they had no idea of their success beyond the islands of the rising sun, so saying that a Japanese mangaka is intending to do a manga that does not cater at all Japan is kind of preposterous.
And, in my opinion, if a new Dragonball storyline was to be produced with the western audiences in mind, I'd be utterly terrified. The amount of franchise pieces from Japan with such premise in mind and failed horribly at it outnumber by far the ones that succeeded.