25% of the second core, not of total power. If the second core is dedicated to WiFi naturally, it's not like it's gotta' be that powerful. After all in the DS the ARM7 was used for WiFi, same sort of scenario (which is likely where this rumor came from)... And Nintendo allowing something like this that would knowingly degrade WiFi? A decrease in processing power like this does no translate to a decrease in range or anything like that, it would translate to dropped packets, meaning disconnects and online games not functioning properly. Why the hell would Nintendo allow that?
As presented, this story is bullshit. Now whether Nintendo's unlocking more power or not I cannot say, but the story as given is bull.
Given that it may affect the communication functions, it could be optional to games which won't use any sort of communication activity and hence they could use that extra processing power. This is all romours as of yet so yeah.