The way I see it, you've got several risks - right now the game has a mix of incentives for people to play. What is being proposed is to temporarily remove all but one of those incentives. If those who don't like PK stop playing for the weekend, you're giving them a reason to go elsewhere; maybe they'll experiment, but really if they don't enjoy PK normally what makes you think they'll enjoy it during an SK-PK weekend?
And running it as a separate copy of SK all the time would just dilute both realms of players.
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One twist to this idea I thought of - maybe some uber pfiles could be created, the name and password to which are the reward for an explorer or quest-completion achievement. A non-PKer would then get to experience a whole slew of PK without ruining their original character's concept, as everyone scrambles to defeat this uber threat to the realms.
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