Alright heres the deal. Namco Bandai was recently in a interveiw and were asked if they would make a Xenosaga IV or possibly a new series of the Xenosaga universe. Here's the interview:

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Question: Any plans on bringing new Xeno series to PS3?

Namco Bandai: The answer for this question is related to earlier questions. There are no plans at this point but we might consider bringing new Xeno series to PS3 if there are huge fan requests and sales.

Question: If Xenosaga Episode III is the last game of the Xenosaga series no matter what, would that change based on fan requests and sales? Is there a chance that Namco Bandai will make more games based on the Xenosaga universe (RPG or not)?

Namco Bandai: Yes, the Xenosaga universe is a grand concept and the number of ways we can think of to expand on this is infinite. We look forward to seeing player's reactions to Xenosaga III, and if reactions are good—who knows!
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What they're saying is, is if we (the fans) give them fan requests they'll make another!

Here's the link for the online petition on the offical NAMCO BANDAI website:

[link]

PLEASE SIGN~!