Sega has officially announced there is indeed a new Shining game for GBA in development, and that footage will be shown at the upcoming TGS.
Entitled Shining Soul, the latest installment of the well-regarded "series" will be an action-RPG--a genre touched in the Shining series only by the oft-maligned Shining Wisdom. In addition to this change, the game will support up to four-players at the same time via Link Cable. Characters will be customizable by class (warrior/magician/archer/berserker), color, and attributes. No other gameplay information has been made available at this time.
While it has been confirmed that Yoshitaka Tamaki will be returning as character designer, no other connection to the previous Shining team has been mentioned.
Currently, the game is slated for a "Spring 2002" release in Japan.