As a strong PrP believer I can still point to these potential issues:
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Access to ST varies between groups. Do you want only specific people shaping the game?
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Timezones are the bane of PrPs. Would you be excluding part of the playerbase from shaping the game?
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Coordination between STs can be a logistical task on its own. Getting/keeping everyone on the same page isn't a trivial challenge.
That's just from the top of my head.