I don't know where it will be, but hopefully it'll be within convenient driving distance of central Pennsylvania.
One thing I'm will to bet on though is that it will take place after May 15, 2007. If I recall correctly, to take advantage of whatever minor bonuses you got as a Fan Club member at C3, your membership had to be valid during the convention.
Right now we're seeing a huge push for new members in the form of this FC President campaign, which ends on May 15th. If C4 takes place say, May 17-20 next year, all the people who sign up now will have to renew their membership to get the FC bonuses.
Call me cynical, but it'd be a brilliant plan on their part to keep Hyperspace membership up through the beginning of 2008 when the real hype/buzz about the TV show will probably start.