Claremont didnt intend for Maddie to be Jean reborn. Thats something he teased with From the Ashes which revealed it to be a hoax by Mastermind. His intent, which he got to play out was that she was a random 1 in a million chance lookalike for Jean. Nothing more beyond that and he did not want Jean resurrected. He definitely could have pitcher Maddie as Jean once he learned of X-Factor but he didnt (instead suggesting Sara Grey be used instead). He was very adamant that Jean stay dead and nearly quit Marvel when he learned she wouldnt bc it undermined what ended up being a very impactful story that he wrote with the DPS
X-Factor had been teasing a Phoenix connection to Maddie and how she may or may not actually be connected to Jean. At the same time, Claremont was building up Sinister in the background and the mystery behind why the mutant hunting Marauders targeted Maddie, a human was unrevealed. That easer for Inferno suggested that these questions would be answered