that doesnt answerExcept for the part where Nomura's already clearly stated that nothing more than the first installment actually occurred to him until development of CoM and KH2 had commenced.
Conclusion: Roxas was very likely not even a loose concept by KH1's completion.
the world that never was
another side another story
the cloaks
riku in asas
roxas in asas
the fact it was left so open ended.
but i do agree that nothing was planned, just that there were openings to play from