Suspicion would've emerged among the shinobi world immediately had an Uchiha with unfathomable power appeared. Presumably, shinobi would've believed him to have been Madara which would've automatically discredited any sort of credibility there was in Pain being the leader of the Akatsuki which is something Obito implicitly wanted. Likewise, he was operating under a false pretense within the Akatsuki and didn't want his colleagues to grow skeptical of him; even Obito didn't feel it was right to reveal his identity to Kisame until after Itachi's death.
Essentially, people would've believed he was Madara, there'd have been little credence in Pain being the leader of the Akatsuki, and he wanted to efface his identity and significance to his colleagues.
I also highly doubt Obito could've captured any of the Jinchuuriki 16 years ago as Chiyo deduced that the only reason the Akatsuki had been snagging Jinchuuriki (post-timeskip) is because they needed to
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. If he wasn't ready now, he wasn't ready 16 years ago. In a sense, Kishimoto predicted and resolved everything in spite of the extra tidbits he added later in the manga.