http://movies.warnerbros.com/pub/mo...x3/matrix3.html
Click on production notes, download the file.
Quote:-
Because Smith's ego and power threaten to overwhelm both the real and Machine worlds, the Oracle chooses to help Neo - a decision that costs her dearly. As it is explained in the video game Enter the Matrix, the Oracle's appearance (or "shell" has been terminated by the vengeful Merovingian, so she takes a new form in Revolutions.
In developing the scripts for Reloaded and Revolutions, the Wachowskis discussed the idea of changing the Oracle's physical appearance, but decided instead to have actress Gloria Foster reprise her role from The Matrix in the second and third chapters of the trilogy. When Foster passed away after completing her scenes for Reloaded, the Brothers returned to their original idea for the path of the Oracle. "Gloria was a remarkably talented, charismatic woman," Silver recalls. "We are extremely proud that she will always be remembered for delivering two of her finest performances in The Matrix and The Matrix Reloaded. Fate forced the Wachowskis to alter the path of the Oracle to address Gloria's passing, but they were able to deepen the character's story as a result and I think it's very effective."
"It was wonderful to see the Brothers find a way to honor Gloria's death and continue growing the story in their changing of the script," Moss agrees.
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So it was their original intention to have Oracle change form.