They don't plan to release Documentation to other Stack Exchange communities at all.
That's not exactly true. Documentation was just launched into public beta last week and before we even consider adding it to other sites we need to make sure it works on Stack Overflow.
That being said it will be some time (6-8 [insert time period here]) before we consider moving it elsewhere. For the time being, I'd suggest contributing to the Salesforce docsSalesforce docs on Stack Overflow.